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NETMOD                                                         L. Lhotka
Internet-Draft                                                    CESNET
Intended status: Standards Track                                 R. Mahy
Expires: September 3, 2010                                   Plantronics
                                                             S. Chisholm
                                                                  Nortel
                                                           March 2, 2010


  Mapping YANG to Document Schema Definition Languages and Validating
                            NETCONF Content
                     draft-ietf-netmod-dsdl-map-05

Abstract

   This draft specifies the mapping rules for translating YANG data
   models into Document Schema Definition Languages (DSDL), a
   coordinated set of XML schema languages standardized as ISO 19757.
   The following DSDL schema languages are used by the mapping: RELAX
   NG, Schematron and DSRL.  The mapping takes one or more YANG modules
   and produces a set of DSDL schemas for a selected target document
   type - datastore content, NETCONF PDU etc.  Procedures for schema-
   based validation of such documents are also discussed.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
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   The list of current Internet-Drafts can be accessed at
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   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on September 3, 2010.

Copyright Notice



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   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the BSD License.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   6
   2.  Terminology and Notation  . . . . . . . . . . . . . . . . . .   7
     2.1.   Glossary of New Terms  . . . . . . . . . . . . . . . . .   8
   3.  Objectives and Motivation . . . . . . . . . . . . . . . . . .  10
   4.  DSDL Schema Languages . . . . . . . . . . . . . . . . . . . .  12
     4.1.   RELAX NG . . . . . . . . . . . . . . . . . . . . . . . .  12
     4.2.   Schematron . . . . . . . . . . . . . . . . . . . . . . .  13
     4.3.   Document Semantics Renaming Language (DSRL)  . . . . . .  14
   5.  Additional Annotations  . . . . . . . . . . . . . . . . . . .  15
     5.1.   Dublin Core Metadata Elements  . . . . . . . . . . . . .  15
     5.2.   RELAX NG DTD Compatibility Annotations . . . . . . . . .  15
     5.3.   NETMOD-Specific Annotations  . . . . . . . . . . . . . .  16
   6.  Overview of the Mapping . . . . . . . . . . . . . . . . . . .  18
   7.  NETCONF Content Validation  . . . . . . . . . . . . . . . . .  20
   8.  Design Considerations . . . . . . . . . . . . . . . . . . . .  21
     8.1.   Conceptual Data Tree . . . . . . . . . . . . . . . . . .  21
     8.2.   Modularity . . . . . . . . . . . . . . . . . . . . . . .  23
     8.3.   Granularity  . . . . . . . . . . . . . . . . . . . . . .  24
     8.4.   Handling of XML Namespaces . . . . . . . . . . . . . . .  24
     8.5.   Features and Deviations  . . . . . . . . . . . . . . . .  25
   9.  Mapping YANG Data Models to the Conceptual Tree Schema  . . .  26
     9.1.   Occurrence Rules for Data Nodes  . . . . . . . . . . . .  26
       9.1.1.    Optional and Mandatory Nodes  . . . . . . . . . . .  27
       9.1.2.    Implicit Nodes  . . . . . . . . . . . . . . . . . .  28
     9.2.   Mapping YANG Groupings and Typedefs  . . . . . . . . . .  29
       9.2.1.    YANG Refinements and Augments . . . . . . . . . . .  31
       9.2.2.    Type Derivation Chains  . . . . . . . . . . . . . .  34
     9.3.   Translation of XPath Expressions . . . . . . . . . . . .  37
     9.4.   YANG Language Extensions . . . . . . . . . . . . . . . .  37
   10. Mapping Conceptual Tree Schema to DSDL  . . . . . . . . . . .  39
     10.1.  Generating RELAX NG Schemas for Various Document Types .  39
       10.1.1.   Reply to <get> or <get-config>  . . . . . . . . . .  40



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       10.1.2.   Remote Procedure Calls  . . . . . . . . . . . . . .  40
       10.1.3.   Notifications . . . . . . . . . . . . . . . . . . .  41
     10.2.  Mapping Semantic Constraints to Schematron . . . . . . .  42
       10.2.1.   Validation Phases . . . . . . . . . . . . . . . . .  45
     10.3.  Constraints on Mandatory Choice  . . . . . . . . . . . .  46
     10.4.  Mapping Default Values to DSRL . . . . . . . . . . . . .  48
   11. Mapping YANG Statements to Conceptual Tree Schema . . . . . .  52
     11.1.  The anyxml Statement . . . . . . . . . . . . . . . . . .  52
     11.2.  The argument Statement . . . . . . . . . . . . . . . . .  53
     11.3.  The augment Statement  . . . . . . . . . . . . . . . . .  54
     11.4.  The base Statement . . . . . . . . . . . . . . . . . . .  54
     11.5.  The belongs-to Statement . . . . . . . . . . . . . . . .  54
     11.6.  The bit Statement  . . . . . . . . . . . . . . . . . . .  54
     11.7.  The case Statement . . . . . . . . . . . . . . . . . . .  54
     11.8.  The choice Statement . . . . . . . . . . . . . . . . . .  54
     11.9.  The config Statement . . . . . . . . . . . . . . . . . .  55
     11.10. The contact Statement  . . . . . . . . . . . . . . . . .  55
     11.11. The container Statement  . . . . . . . . . . . . . . . .  55
     11.12. The default Statement  . . . . . . . . . . . . . . . . .  55
     11.13. The description Statement  . . . . . . . . . . . . . . .  57
     11.14. The deviation Statement  . . . . . . . . . . . . . . . .  57
     11.15. The enum Statement . . . . . . . . . . . . . . . . . . .  57
     11.16. The error-app-tag Statement  . . . . . . . . . . . . . .  57
     11.17. The error-message Statement  . . . . . . . . . . . . . .  57
     11.18. The extension Statement  . . . . . . . . . . . . . . . .  57
     11.19. The feature Statement  . . . . . . . . . . . . . . . . .  57
     11.20. The grouping Statement . . . . . . . . . . . . . . . . .  57
     11.21. The identity Statement . . . . . . . . . . . . . . . . .  58
     11.22. The if-feature Statement . . . . . . . . . . . . . . . .  58
     11.23. The import Statement . . . . . . . . . . . . . . . . . .  58
     11.24. The include Statement  . . . . . . . . . . . . . . . . .  58
     11.25. The input Statement  . . . . . . . . . . . . . . . . . .  59
     11.26. The key Statement  . . . . . . . . . . . . . . . . . . .  59
     11.27. The leaf Statement . . . . . . . . . . . . . . . . . . .  59
     11.28. The leaf-list Statement  . . . . . . . . . . . . . . . .  59
     11.29. The length Statement . . . . . . . . . . . . . . . . . .  60
     11.30. The list Statement . . . . . . . . . . . . . . . . . . .  60
     11.31. The mandatory Statement  . . . . . . . . . . . . . . . .  61
     11.32. The max-elements Statement . . . . . . . . . . . . . . .  61
     11.33. The min-elements Statement . . . . . . . . . . . . . . .  62
     11.34. The module Statement . . . . . . . . . . . . . . . . . .  62
     11.35. The must Statement . . . . . . . . . . . . . . . . . . .  62
     11.36. The namespace Statement  . . . . . . . . . . . . . . . .  63
     11.37. The notification Statement . . . . . . . . . . . . . . .  63
     11.38. The ordered-by Statement . . . . . . . . . . . . . . . .  63
     11.39. The organization Statement . . . . . . . . . . . . . . .  63
     11.40. The output Statement . . . . . . . . . . . . . . . . . .  63
     11.41. The path Statement . . . . . . . . . . . . . . . . . . .  63



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     11.42. The pattern Statement  . . . . . . . . . . . . . . . . .  64
     11.43. The position Statement . . . . . . . . . . . . . . . . .  64
     11.44. The prefix Statement . . . . . . . . . . . . . . . . . .  64
     11.45. The presence Statement . . . . . . . . . . . . . . . . .  64
     11.46. The range Statement  . . . . . . . . . . . . . . . . . .  64
     11.47. The reference Statement  . . . . . . . . . . . . . . . .  64
     11.48. The require-instance Statement . . . . . . . . . . . . .  64
     11.49. The revision Statement . . . . . . . . . . . . . . . . .  64
     11.50. The rpc Statement  . . . . . . . . . . . . . . . . . . .  65
     11.51. The status Statement . . . . . . . . . . . . . . . . . .  65
     11.52. The submodule Statement  . . . . . . . . . . . . . . . .  65
     11.53. The type Statement . . . . . . . . . . . . . . . . . . .  65
       11.53.1.  The empty Type  . . . . . . . . . . . . . . . . . .  66
       11.53.2.  The boolean and binary Types  . . . . . . . . . . .  67
       11.53.3.  The bits Type . . . . . . . . . . . . . . . . . . .  67
       11.53.4.  The enumeration and union Types . . . . . . . . . .  67
       11.53.5.  The identityref Type  . . . . . . . . . . . . . . .  67
       11.53.6.  The instance-identifier Type  . . . . . . . . . . .  69
       11.53.7.  The leafref Type  . . . . . . . . . . . . . . . . .  69
       11.53.8.  The numeric Types . . . . . . . . . . . . . . . . .  69
       11.53.9.  The string Type . . . . . . . . . . . . . . . . . .  71
       11.53.10. Derived Types . . . . . . . . . . . . . . . . . . .  72
     11.54. The typedef Statement  . . . . . . . . . . . . . . . . .  73
     11.55. The unique Statement . . . . . . . . . . . . . . . . . .  73
     11.56. The units Statement  . . . . . . . . . . . . . . . . . .  73
     11.57. The uses Statement . . . . . . . . . . . . . . . . . . .  74
     11.58. The value Statement  . . . . . . . . . . . . . . . . . .  74
     11.59. The when Statement . . . . . . . . . . . . . . . . . . .  74
     11.60. The yang-version Statement . . . . . . . . . . . . . . .  74
     11.61. The yin-element Statement  . . . . . . . . . . . . . . .  74
   12. Mapping NETMOD-specific annotations to DSDL Schema
       Languages . . . . . . . . . . . . . . . . . . . . . . . . . .  75
     12.1.  The @nma:config Annotation . . . . . . . . . . . . . . .  75
     12.2.  The @nma:default Annotation  . . . . . . . . . . . . . .  75
     12.3.  The @nma:implicit Annotation . . . . . . . . . . . . . .  75
     12.4.  The <nma:error-app-tag> Annotation . . . . . . . . . . .  75
     12.5.  The <nma:error-message> Annotation . . . . . . . . . . .  75
     12.6.  The <nma:instance-identifier> Annotation . . . . . . . .  75
     12.7.  The @nma:key Annotation  . . . . . . . . . . . . . . . .  76
     12.8.  The @nma:leafref Annotation  . . . . . . . . . . . . . .  76
     12.9.  The @nma:min-elements Annotation . . . . . . . . . . . .  76
     12.10. The @nma:max-elements Annotation . . . . . . . . . . . .  77
     12.11. The <nma:must> Annotation  . . . . . . . . . . . . . . .  77
     12.12. The <nma:ordered-by> Annotation  . . . . . . . . . . . .  77
     12.13. The <nma:status> Annotation  . . . . . . . . . . . . . .  77
     12.14. The @nma:unique Annotation . . . . . . . . . . . . . . .  77
     12.15. The @nma:when Annotation . . . . . . . . . . . . . . . .  78
   13. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  79



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   14. Security Considerations . . . . . . . . . . . . . . . . . . .  80
   15. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  81
   16. References  . . . . . . . . . . . . . . . . . . . . . . . . .  82
     16.1.  Normative References . . . . . . . . . . . . . . . . . .  82
     16.2.  Informative References . . . . . . . . . . . . . . . . .  83
   Appendix A.  Schemas for NETMOD-Specific Annotations  . . . . . .  86
     A.1.   NVDL Schema  . . . . . . . . . . . . . . . . . . . . . .  86
     A.2.   Annotation Attributes for define Pattern . . . . . . . .  88
     A.3.   Annotation Elements for element Pattern  . . . . . . . .  88
     A.4.   Annotation Attributes for element Pattern  . . . . . . .  89
     A.5.   Annotation attributes for group Pattern  . . . . . . . .  89
     A.6.   Annotation attributes for choice and ref Patterns  . . .  90
     A.7.   Annotation attributes for element Pattern in the List
            Context  . . . . . . . . . . . . . . . . . . . . . . . .  90
     A.8.   Annotation attributes for value Pattern  . . . . . . . .  91
     A.9.   Named Patterns for All NETMOD-Specific Annotations . . .  91
   Appendix B.  Schema-Independent Library . . . . . . . . . . . . .  95
   Appendix C.  Mapping DHCP Data Model - A Complete Example . . . .  96
     C.1.   Input YANG Module  . . . . . . . . . . . . . . . . . . .  96
     C.2.   Conceptual Tree Schema . . . . . . . . . . . . . . . . .  99
       C.2.1.    XML Syntax  . . . . . . . . . . . . . . . . . . . .  99
       C.2.2.    Compact Syntax  . . . . . . . . . . . . . . . . . . 104
     C.3.   Final DSDL Schemas . . . . . . . . . . . . . . . . . . . 106
       C.3.1.    RELAX NG Schema for <get> Reply - XML Syntax  . . . 107
       C.3.2.    RELAX NG Schema for <get> Reply - Compact Syntax  . 111
     C.4.   Schematron Schema for <get> Reply  . . . . . . . . . . . 113
     C.5.   DSRL Schema for <get> Reply  . . . . . . . . . . . . . . 115
   Appendix D.  Change Log . . . . . . . . . . . . . . . . . . . . . 116
     D.1.   Changes Between Versions -04 and -05 . . . . . . . . . . 116
     D.2.   Changes Between Versions -03 and -04 . . . . . . . . . . 116
     D.3.   Changes Between Versions -02 and -03 . . . . . . . . . . 117
     D.4.   Changes Between Versions -01 and -02 . . . . . . . . . . 117
     D.5.   Changes Between Versions -00 and -01 . . . . . . . . . . 118
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . 119

















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1.  Introduction

   The NETCONF Working Group has completed a base protocol used for
   configuration management [RFC4741].  This base specification defines
   protocol bindings and an XML container syntax for configuration and
   management operations, but does not include a modeling language or
   accompanying rules for how to model configuration and status
   information (in XML syntax) carried by NETCONF.  The IETF Operations
   Area has a long tradition of defining data for SNMP Management
   Information Bases (MIBs) [RFC1157] using the SMI language [RFC2578]
   to model its data.  While this specific modeling approach has a
   number of well-understood problems, most of the data modeling
   features provided by SMI are still considered extremely important.
   Simply modeling the valid syntax without the additional semantic
   relationships has caused significant interoperability problems in the
   past.

   The NETCONF community concluded that a data modeling framework is
   needed to support ongoing development of IETF and vendor-defined
   management information modules.  The NETMOD Working Group was
   chartered to address this problem by defining a new human-friendly
   modeling language based on SMIng [RFC3216] and called YANG [YANG].

   Since NETCONF uses XML for encoding its protocol data units (PDU), it
   is natural to express the constraints on NETCONF content using
   standard XML schema languages.  For this purpose, the NETMOD WG
   selected the Document Schema Definition Languages (DSDL) that is
   being standardized as ISO/IEC 19757 [DSDL].  The DSDL framework
   comprises a set of XML schema languages that address grammar rules,
   semantic constraints and other data modeling aspects but also, and
   more importantly, do it in a coordinated and consistent way.  While
   it is true that some DSDL parts have not been standardized yet and
   are still work in progress, the three parts that the YANG-to-DSDL
   mapping relies upon - RELAX NG, Schematron and DSRL - already have
   the status of an ISO/IEC International Standard and are supported in
   a number of software tools.

   This document contains specification of a mapping that translates
   YANG data models to XML schemas utilizing a subset of the DSDL schema
   languages.  The mapping procedure is divided into two steps: In the
   first step, the structure of the data tree, RPC signatures and
   notifications is expressed as a single RELAX NG grammar with simple
   annotations representing additional data model information (metadata,
   documentation, semantic constraints, default values etc.).  The
   second step then generates a coordinated set of DSDL schemas that can
   validate specific XML documents such as client requests, server
   responses or notifications, perhaps also taking into account
   additional context such as active capabilities.



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2.  Terminology and Notation

   This document relies on many terms that are defined in the
   specifications of the NETCONF protocol [RFC4741] and YANG data
   modeling language [YANG].  Also, the common terminology of XML and
   DSDL schema languages is used as defined in the respective standards
   [XML], [DSDL], [NVDL], [RNG], [Schematron] and [DSRL].

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   In the text, we use the following typographic conventions:

   o  YANG statement keywords are delimited by single quotes.

   o  XML element names are delimited by "<" and ">" characters.

   o  Names of XML attributes are prefixed by the "@" character.

   o  Other literal values are delimited by double quotes.

   XML elements names are always written with explicit namespace
   prefixes corresponding to the following XML vocabularies:

   "a"  DTD compatibility annotations [RNG-DTD];

   "dc"  Dublin Core metadata elements [RFC5013];

   "dsrl"  Document Semantics Renaming Language [DSRL];

   "en"  NETCONF event notifications [RFC5277];

   "nc"  NETCONF protocol [RFC4741];

   "nma"  NETMOD-specific schema annotations (see Section 5.3);

   "nmf"  NETMOD-specific XPath extension functions (see Section 12.6);

   "nmt"  Conceptual tree (see Section 8.1);

   "rng"  RELAX NG [RNG];

   "sch"  ISO Schematron [Schematron];







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   "xsd"  W3C XML Schema [XSD].

   The following table shows the mapping of these prefixes to namespace
   URIs.

     +--------+-----------------------------------------------------+
     | Prefix | Namespace URI                                       |
     +--------+-----------------------------------------------------+
     | a      | http://relaxng.org/ns/compatibility/annotations/1.0 |
     |        |                                                     |
     | dc     | http://purl.org/dc/terms                            |
     |        |                                                     |
     | dsrl   | http://purl.oclc.org/dsdl/dsrl                      |
     |        |                                                     |
     | en     | urn:ietf:params:xml:ns:netconf:notification:1.0     |
     |        |                                                     |
     | nc     | urn:ietf:params:xml:ns:netconf:base:1.0             |
     |        |                                                     |
     | nma    | urn:ietf:params:xml:ns:netmod:dsdl-annotations:1    |
     |        |                                                     |
     | nmf    | urn:ietf:params:xml:ns:netmod:xpath-extensions:1    |
     |        |                                                     |
     | nmt    | urn:ietf:params:xml:ns:netmod:conceptual-tree:1     |
     |        |                                                     |
     | rng    | http://relaxng.org/ns/structure/1.0                 |
     |        |                                                     |
     | sch    | http://purl.oclc.org/dsdl/schematron                |
     |        |                                                     |
     | xsd    | http://www.w3.org/2001/XMLSchema                    |
     +--------+-----------------------------------------------------+

          Table 1: Used namespace prefixes and corresponding URIs

2.1.  Glossary of New Terms

   o  ancestor datatype: Any datytype a given datatype is (transitively)
      derived from.

   o  ancestor built-in datatype: The built-in datatype that is at the
      start of the type derivation chain for a given datatype.

   o  conceptual data tree: A virtual XML document integrating all
      components of a YANG data model, i.e., configuration datastore,
      RPC methods (both requests and replies) and notifications.  The
      conceptual tree is normally not instantiated, it only serves as a
      conceptual target for its schema.  See Section 8.1 for details.





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   o  implicit node: A node that, if missing, may be added to the
      information set of an XML document (configuration, RPC input or
      output, notification) without changing the meaning of that XML
      document.















































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3.  Objectives and Motivation

   The main objective of this work is to complement YANG as a data
   modeling language by validation capabilities of DSDL schema
   languages, namely RELAX NG, Schematron and DSRL.  This document
   describes the correspondence between grammatical, semantic and data
   type constraints expressed in YANG and equivalent DSDL constructs.
   The ultimate goal is to be able to capture all substantial
   information contained in YANG modules and express it in DSDL schemas.
   While the mapping from YANG to DSDL described in this document is in
   principle invertible, the inverse mapping from DSDL to YANG is not in
   its scope.

   XML-based information models and XML-encoded data appear in several
   different forms in various phases of YANG data modeling and NETCONF
   workflow - configuration datastore contents, RPC requests and
   replies, and notifications.  Moreover, RPC methods are characterized
   by an inherent diversity resulting from selective availability of
   capabilities and features.  YANG modules can also define new RPC
   methods.  The mapping should be able to accommodate this variability
   and generate schemas that are specifically tailored to a particular
   situation and thus considerably more effective for validation than
   generic all-encompassing schemas.

   In order to cope with this variability, we assume that the schemas
   can be generated on demand for a particular purpose from the
   available collection of YANG modules and their lifetime will be
   relatively short.  In other words, we don't envision that any
   collection of DSDL schemas will be created and maintained over an
   extended period of time in parallel to YANG modules.

   The generated schemas are primarily intended as input to the existing
   XML schema validators and other off-the-shelf tools.  However, the
   schemas may also be perused by developers and users as a formal
   representation of constraints on a particular XML-encoded data
   object.  Consequently, our secondary goal is to keep the schemas as
   readable as possible.  To this end, the complexity of the mapping is
   distributed into two steps:

   1.  The first step maps one or more YANG modules to a single RELAX NG
       schema of the so-called "conceptual tree", which contains
       grammatical constraints for the main data tree as well as RPCs
       and notifications.  In order to record additional constraints
       that appear in the YANG modules but cannot be expressed in RELAX
       NG, the schema is augmented by simple annotations.  The output of
       the first step can thus be considered a reasonably readable
       equivalent of the input YANG modules.




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   2.  In the second step, the annotated RELAX NG schema from step 1 is
       transformed further to a coordinated set of fully conformant DSDL
       schemas containing constraints for a particular data object and a
       specific situation.  The DSDL schemas are intended mainly for
       machine validation using off-the-shelf tools.














































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4.  DSDL Schema Languages

   Document Schema Definition Languages (DSDL) is a framework of schema
   languages that is being developed as an international standard ISO/
   IEC 19757.  Unlike other approaches to XML document validation, most
   notably W3C XML Schema (XSD) [XSD], the DSDL framework adheres to the
   principle of "small languages": Each of the DSDL constituents is a
   stand-alone schema language with a relatively narrow purpose and
   focus.  Together, these schema languages may be used in a coordinated
   way to accomplish various validation tasks.

   The mapping described in this document uses three of the DSDL schema
   languages, namely RELAX NG, Schematron and DSRL.

4.1.  RELAX NG

   RELAX NG (pronounced "relaxing") is an XML schema language for
   grammar-based validation and Part 2 of the ISO/IEC DSDL family of
   standards [RNG].  Like the W3C XML Schema language [XSD], it is able
   to describe constraints on the structure and content of XML
   documents.  However, unlike the DTD [XML] and XSD schema languages,
   RELAX NG intentionally avoids any infoset augmentation such as
   defining default values.  In the DSDL architecture, the particular
   task of defining and applying default values is delegated to another
   schema language, DSRL (see Section 4.3).

   As its base datatype library, RELAX NG uses the W3C XML Schema
   Datatype Library [XSD-D], but unlike XSD, other datatype libraries
   may be used along with it or even replace it if necessary.

   RELAX NG is very liberal in accepting annotations from other
   namespaces.  With few exceptions, such annotations may be placed
   anywhere in the schema and need no encapsulating elements such as
   <xsd:annotation> in XSD.

   RELAX NG schemas can be represented in two equivalent syntaxes: XML
   and compact.  The compact syntax is described in Annex C of the RELAX
   NG specification [RNG-CS], which was added to the standard in 2006
   (Amendment 1).  Automatic bidirectional conversions between the two
   syntaxes can be accomplished using several tools, for example
   Trang [1].

   For its terseness and readability, the compact syntax is often the
   preferred form for publishing RELAX NG schemas whereas validators and
   other software tools usually work with the XML syntax.  However, the
   compact syntax has two drawbacks:





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   o  External annotations make the compact syntax schema considerably
      less readable.  While in the XML syntax the annotating elements
      and attributes are represented in a simple and uniform way (XML
      elements and attributes from foreign namespaces), the compact
      syntax uses four different syntactic constructs: documentation,
      grammar, initial and following annotations.  Therefore, the impact
      of annotations on readability is often much stronger for the
      compact syntax than for the XML syntax.

   o  In a computer program, it is more difficult to generate the
      compact syntax than the XML syntax.  While a number of software
      libraries exist that make it easy to create an XML tree in memory
      and serialize it, no such aid is available for compact syntax.

   For these reasons, the mapping specification in this document uses
   exclusively the XML syntax.  Where appropriate, though, the schemas
   resulting from the translation may be presented in the equivalent
   compact syntax.

   RELAX NG elements are qualified with the namespace URI
   "http://relaxng.org/ns/structure/1.0".  The namespace of the W3C
   Schema Datatype Library is
   "http://www.w3.org/2001/XMLSchema-datatypes".

4.2.  Schematron

   Schematron is Part 3 of DSDL that reached the status of a full ISO/
   IEC standard in 2006 [Schematron].  In contrast to the traditional
   schema languages such as DTD, XSD or RELAX NG, which are based on the
   concept of a formal grammar, Schematron utilizes a rule-based
   approach.  Its rules may specify arbitrary conditions involving data
   from different parts of an XML document.  Each rule consists of three
   essential components:

   o  context - an XPath expression that defines the set of locations
      where the rule is to be applied;

   o  assert or report condition - another XPath expression that is
      evaluated relative to the location matched by the context
      expression;

   o  human-readable message that is displayed when the assert condition
      is false or report condition is true.

   The difference between the assert and report condition is that the
   former is positive in that it states a condition that a valid
   document has to satisfy, whereas the latter specifies an error
   condition.



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   Schematron draws most of its expressive power from XPath [XPath] and
   XSLT [XSLT].  ISO Schematron allows for dynamic query language
   binding so that the following XML query languages can be used: STX,
   XSLT 1.0, XSLT 1.1, EXSLT, XSLT 2.0, XPath 1.0, XPath 2.0 and
   XQuery 1.0 (this list may be extended in the future).

   The human-readable error messages are another feature that
   distinguishes Schematron from other common schema languages.  The
   messages may even contain XPath expressions that are evaluated in the
   actual context and thus refer to existing XML document nodes and
   their contents.

   The rules defined by a Schematron schema may be divided into several
   subsets known as phases.  Validations may then be set up to include
   only selected phases.  In the context of NETCONF data validation,
   this is useful for relaxing constraints that may not always apply.
   For example, the reference integrity may not be enforced for a
   candidate configuration.

   Schematron elements are qualified with namespace URI
   "http://purl.oclc.org/dsdl/schematron".

4.3.  Document Semantics Renaming Language (DSRL)

   DSRL (pronounced "disrule") is Part 8 of DSDL that reached the status
   of a full ISO/IEC standard in 2008 [DSRL].  Unlike RELAX NG and
   Schematron, it is specifically designed to modify XML information set
   of the validated document.  While DSRL is primarily intended for
   renaming XML elements and attributes, it can also define default
   values for XML attributes and default content for XML elements so
   that elements or attributes with these default values are inserted if
   they are missing (or present and empty) in the validated documents.
   The latter feature is used by the YANG-to-DSDL mapping for
   representing YANG default contents consisting of leaf nodes with
   default values and their ancestor non-presence containers.

   DSRL elements are qualified with namespace URI
   "http://purl.oclc.org/dsdl/dsrl".













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5.  Additional Annotations

   Besides the DSDL schema languages, the mapping also uses three sets
   of annotations that are added as foreign-namespace attributes and
   elements to RELAX NG schemas.  Two of the annotation sets - Dublin
   Core elements and DTD compatibility annotations - are standard
   vocabularies for representing metadata and documentation,
   respectively.  Although these data model items are not used for
   formal validation, they quite often carry important information for
   data model implementers.  Therefore, they SHOULD be included in the
   conceptual tree schema and MAY also appear in the final validation
   schemas.

   The third set are NETMOD-specific annotations conveying YANG semantic
   constraints and other information that cannot be expressed directly
   in RELAX NG.  These annotations are only used in the first step of
   the mapping, i.e., in the conceptual tree schema.  In the second
   mapping step, these annotations are converted to Schematron and DSRL
   rules.

5.1.  Dublin Core Metadata Elements

   Dublin Core [2] is a system of metadata elements that was originally
   created for describing metadata of World Wide Web resources in order
   to facilitate their automated lookup.  Later it was accepted as a
   standard for describing metadata of arbitrary resources.  This
   specification uses the definition from [RFC5013].

   Dublin Core elements are qualified with namespace URI
   "http://purl.org/dc/terms".

5.2.  RELAX NG DTD Compatibility Annotations

   DTD compatibility annotations are part of the RELAX NG DTD
   Compatibility specification [RNG-DTD].  YANG-to-DSDL mapping uses
   only the <a:documentation> annotation for representing YANG
   'description' and 'reference' texts.

   Note that there is no intention to make the resulting schemas DTD-
   compatible, the main reason for using these annotations is technical:
   they are well supported and adequately interpreted by several RELAX
   NG tools.

   DTD compatibility annotations are qualified with namespace URI
   "http://relaxng.org/ns/compatibility/annotations/1.0".






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5.3.  NETMOD-Specific Annotations

   NETMOD-specific annotations are XML elements and attributes qualified
   with the namespace URI
   "urn:ietf:params:xml:ns:netmod:dsdl-annotations:1" that appear in
   various locations of the conceptual tree schema.  YANG statements are
   mapped to these annotations in a straightforward way.  In most cases,
   the annotation attributes and elements have the same name as the
   corresponding YANG statement.

   Table 2 lists alphabetically the names of NETMOD-specific annotation
   attributes (prefixed with "@") and elements (in angle brackets) along
   with a reference to the section where their use is described.
   Appendix A contains the formal specification of this annotation
   vocabulary.




































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         +---------------------------+--------------------+------+
         | annotation                | section            | note |
         +---------------------------+--------------------+------+
         | @nma:config               | 11.9               |      |
         |                           |                    |      |
         | @nma:default              | 11.12              |      |
         |                           |                    |      |
         | @nma:implicit             | 11.11, 11.7, 11.12 |      |
         |                           |                    |      |
         | <nma:error-app-tag>       | 11.16              | 1    |
         |                           |                    |      |
         | <nma:error-message>       | 11.17              | 1    |
         |                           |                    |      |
         | <nma:instance-identifier> | 11.53.6            | 2    |
         |                           |                    |      |
         | @nma:key                  | 11.26              |      |
         |                           |                    |      |
         | @nma:leafref              | 11.53.7            |      |
         |                           |                    |      |
         | @nma:min-elements         | 11.28              |      |
         |                           |                    |      |
         | @nma:max-elements         | 11.28              |      |
         |                           |                    |      |
         | <nma:must>                | 11.35              | 3    |
         |                           |                    |      |
         | @nma:ordered-by           | 11.38              |      |
         |                           |                    |      |
         | @nma:presence             | 11.45              |      |
         |                           |                    |      |
         | @nma:status               | 11.51              |      |
         |                           |                    |      |
         | @nma:unique               | 11.55              |      |
         |                           |                    |      |
         | @nma:units                | 11.56              |      |
         |                           |                    |      |
         | @nma:when                 | 11.59              |      |
         +---------------------------+--------------------+------+

                   Table 2: NETMOD-specific annotations

   Notes:

   1.  Appears only as subelement of <nma:must>.

   2.  Has an optional attribute @require-instance.

   3.  Has a mandatory attribute @assert and two optional subelements
       <nma:error-app-tag> and <nma:error-message>.



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6.  Overview of the Mapping

   This section gives an overview of the YANG-to-DSDL mapping, its
   inputs and outputs.  Figure 1 presents an overall structure of the
   mapping:

                    +----------------+
                    | YANG module(s) |
                    +----------------+
                            |
                            |T
                            |
          +-------------------------------------+
          | RELAX NG schema for conceptual tree |
          +-------------------------------------+
               /       |           |       \
              /        |           |        \        +-------+
           Tg/       Tr|           |Tn       \       |library|
            /          |           |          \      +-------+
      +---------+   +-----+    +-------+    +------+
      |get reply|   | rpc |    | notif |    | .... |
      +---------+   +-----+    +-------+    +------+

                    Figure 1: Structure of the mapping

   The mapping procedure is divided into two steps:

   1.  Transformation T in the first step maps one or more YANG modules
       to a single RELAX NG schema for the conceptual tree (see
       Section 8.1).  Constraints that cannot be expressed directly in
       RELAX NG (list key definitions, 'must' statements etc.) and
       various documentation texts are recorded in the schema as
       foreign-namespace annotations.

   2.  In the second step, the conceptual tree schema is transformed in
       multiple ways to a coordinated set of DSDL schemas that can be
       used for validating a particular data object in a specific
       context.  Figure 1 shows just three simple possibilities as
       examples.  In the process, appropriate parts of the conceptual
       tree schema are extracted and specific annotations transformed to
       equivalent, but usually more complex, Schematron patterns, DSRL
       element maps etc.

   3.  As indicated in Figure 1, the second step of the mapping also
       uses a schema-independent library that contains common schema
       objects such as RELAX NG named pattern definitions.

   An implementation of the mapping algorithm is supposed to accept one



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   or more valid YANG modules as its input.  It is important to be able
   to process multiple YANG modules together since multiple modules may
   be negotiated for a NETCONF session and the contents of the
   configuration datastore is then obtained as the union of data trees
   specified by the individual modules, which may also lead to multiple
   roots.  In addition, the input modules may be further coupled by the
   'augment' statement in which one module augments the data tree of
   another module.

   It is also assumed that the algorithm has access, perhaps on demand,
   to all YANG modules that the input modules import (perhaps
   transitively).

   The output of the first mapping step is an annotated RELAX NG schema
   for the conceptual tree - a virtual XML document containing, in its
   different subtrees, the entire datastore, all RPC requests and
   replies, and notifications as defined by the input YANG modules.  By
   "virtual" we mean that such an XML document need not correspond to
   the actual layout of the configuration database in a NETCONF server,
   and will certainly never appear on the wire as the content of a
   NETCONF PDU.  Hence, the RELAX NG schema for the conceptual tree is
   not intended for any direct validations but rather as a
   representation of a particular data model expressed in annotated
   RELAX NG and the common starting point for subsequent transformations
   that may produce practical validation schemas.  The conceptual tree
   is further described in Section 8.1.

   Other information contained in input YANG modules, such as semantic
   constraints or default values, are recorded in the conceptual tree
   schema as annotations - XML attributes or elements qualified with
   namespace URI "urn:ietf:params:xml:ns:netmod:dsdl-annotations:1".
   Metadata describing the YANG modules are mapped to annotations
   utilizing Dublin Core elements (Section 5.1).  Finally, documentation
   strings are mapped to <a:documentation> elements belonging to the DTD
   compatibility vocabulary (Section 5.2).

   The output from the second step is a coordinated set of three DSDL
   schemas corresponding to a specific data object and context:

   o  RELAX NG schema describing the grammatical and datatype
      constraints;

   o  Schematron schema expressing other constraints such as uniqueness
      of list keys or user-specified semantic rules;

   o  DSRL schema containing the specification of default contents.





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7.  NETCONF Content Validation

   This section describes how the schemas generated by the YANG-to-DSDL
   mapping are supposed to be applied for validating XML instance
   documents such as the content of a datastore or various NETCONF PDUs.

   The validation proceeds in the following steps, which are also
   illustrated in Figure 2:

   1.  The XML instance document can be immediately checked for
       grammatical and data type validity using the RELAX NG schema.

   2.  Second, default values for leaf nodes have to be applied and
       their ancestor containers added where necessary.  It is important
       to add the implicit nodes before the next validation step because
       YANG specification [YANG] states that the data tree against which
       XPath expressions are evaluated already has all defaults
       filled-in.  Note that this step modifies the information set of
       the validated XML document.

   3.  The semantic constraints are checked using the Schematron schema.


         +----------+                        +----------+
         |          |                        |   XML    |
         |   XML    |                        | document |
         | document |-----------o----------->|   with   |
         |          |           ^            | defaults |
         |          |           |            |          |
         +----------+           |            +----------+
              ^                 | filling-in       ^
              | grammar,        | defaults         | semantic
              | datatypes       |                  | constraints
              |                 |                  |
         +----------+       +--------+       +------------+
         | RELAX NG |       |  DSRL  |       | Schematron |
         |  schema  |       | schema |       |   schema   |
         +----------+       +--------+       +------------+

               Figure 2: Outline of the validation procedure











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8.  Design Considerations

   YANG modules could in principle be mapped to DSDL schemas in a number
   of ways.  The mapping procedure described in this document uses
   several specific design decisions that are discussed in the following
   subsections.

8.1.  Conceptual Data Tree

   DSDL schemas generated from YANG modules using the procedure
   described in this document are intended to be used for validating
   XML-encoded NETCONF data in various forms: every YANG-based model
   represents the contents of a datastore but also implies an array of
   schemas for all types of NETCONF PDUs.  For a reasonably strict
   validation of a given data object, the schemas have to be quite
   specific.  To begin with, effective validation of NETCONF PDU content
   requires separation of client and server schemas.  While the decision
   about proper structuring of all PDU-validating schemas is beyond the
   scope of this document, the mapping procedure is designed to
   accommodate any foreseeable validation needs.

   An essential part of the YANG-to-DSDL mapping procedure is
   nonetheless common to all validation needs: the grammar and datatype
   specifications for the datastore, RPCs and notifications expressed by
   one or more YANG modules have to be translated to RELAX NG.  In order
   to be able to separate this common step, we introduce the notion of
   conceptual data tree: it is a virtual XML tree that contains full
   datastore, RPC requests with corresponding replies and notifications.
   The schema for the conceptual tree - a single RELAX NG schema with
   annotations - therefore has a quite similar logic as the input YANG
   module(s), the only major difference being the RELAX NG schema
   language.

   For example, the conceptual data tree for a YANG module defining
   nodes in the namespace "http://example.com/ns/example" may be
   schematically represented as follows:















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   <nmt:netmod-tree
       xmlns:nmt="urn:ietf:params:xml:ns:netmod:conceptual-tree:1"
       xmlns:ex="http://example.com/ns/example">
     <nmt:top>
       ... configuration and status data ...
     </nmt:top>
     <nmt:rpc-methods>
       <nmt:rpc-method>
         <nmt:input>
           <ex:myrpc ...>
             ...
           </myrpc>
         </nmt:input>
         <nmt:output>
           ...
         </nmt:output>
       </nmt:rpc-method>
       ...
     </nmt:rpc-methods>
     <nmt:notifications>
       <nmt:notification>
         <ex:mynotif>
           ...
         </mynotif>
       </nmt:notification>
       ...
     </nmt:notifications>
   </nmt:netmod>

   The namespace URI "urn:ietf:params:xml:ns:netmod:conceptual-tree:1"
   identifies a simple vocabulary consisting of a few elements that
   encapsulate and separate the various parts of the conceptual data
   tree.

   The conceptual tree schema is not intended for direct validation but
   rather serves as a well-defined starting point for subsequent
   transformations that generate validation schemas.  In general, these
   transformations should be relatively simple - they will typically
   extract one or more subtrees from the conceptual tree schema, modify
   them as necessary and add encapsulating elements such as those from
   the NETCONF RPC layer.

   Additional information contained in the source YANG module(s), such
   as semantic constraints and default values, is represented in the
   form of interim NETMOD-specific annotations that are included as
   foreign-namespace elements or attributes in the RELAX NG schema for
   the conceptual tree.  In the second phase of the mapping, these
   annotations are typically translated to equivalent Schematron and



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   DSRL rules.

   As a useful side effect, by introducing the conceptual data tree we
   are also able to resolve the difficulties arising from the fact that
   a single datastore may consist of multiple parallel data hierarchies
   defined in one or more YANG modules, which cannot be mapped to a
   valid XML document.  In the conceptual data tree, such multiple
   hierarchies appear under the single <nmt:top> element.

8.2.  Modularity

   Both YANG and RELAX NG offer means for modularity, i.e., for
   splitting the contents of a full schema into separate modules and
   combining or reusing them in various ways.  However, the approaches
   taken by YANG and RELAX NG differ.  Modularity in RELAX NG is
   suitable for ad hoc combinations of a small number of schemas whereas
   YANG assumes a large set of modules similar to SNMP MIBs.  The
   following differences are important:

   o  In YANG, whenever module A imports module B, it gets access to the
      definitions (groupings and typedefs) appearing at the top level of
      module B. However, no part of data tree from module B is imported
      along with it.  In contrast, the <rng:include> pattern in RELAX NG
      imports both definitions of named patterns and the entire schema
      tree from the included schema.

   o  The names of imported YANG groupings and typedefs are qualified
      with the namespace of the imported module.  On the other hand, the
      names of data nodes contained inside the imported groupings, when
      used within the importing module, become part of the importing
      module's namespace.  In RELAX NG, the names of patterns are
      unqualified and so named patterns defined in both the importing
      and imported module share the same flat namespace.  The contents
      of RELAX NG named patterns may either keep the namespace of the
      schema where they are defined or inherit the namespace of the
      importing module, analogically to YANG.  However, in order to
      achieve the latter behavior, the imported module must be prepared
      in a special way as a library module that cannot be used as a
      stand-alone schema.

   So the conclusion is that the modularity mechanisms of YANG and RELAX
   NG, albeit similar, are not directly compatible.  Therefore, the
   corresponding design decision for the mapping algorithm is to collect
   all information in a single schema for the conceptual tree, even if
   it comes from multiple YANG modules or submodules.  In other words,
   translations of imported groupings and typedefs are installed in the
   translation of importing module - but only if they are really used
   there.



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   NOTE: The 'include' statement that is used in YANG for including
   submodules has in fact the same semantics as the <rng:include>
   pattern.  However, since we don't map the modular structure for YANG
   modules, it seems to have little sense to do it for submodules.
   Consequently, the contents of submodules appear directly in the
   conceptual tree schema, too.

8.3.  Granularity

   RELAX NG supports different styles of schema structuring: One
   extreme, often called "Russian Doll", specifies the structure of an
   XML instance document in a single hierarchy.  The other extreme, the
   flat style, uses a similar approach as the Data Type Definition (DTD)
   schema language - every XML element corresponds to a named pattern
   definition.  In practice, some compromise between the two extremes is
   usually chosen.

   YANG supports both styles in principle, too, but in most cases the
   modules are organized in a way that's closer to the "Russian Doll"
   style, which provides a better insight into the structure of the
   configuration data.  Groupings are usually defined only for contents
   that are prepared for reuse in multiple places via the 'uses'
   statement.  In contrast, RELAX NG schemas tend to be much flatter,
   because finer granularity is also needed in RELAX NG for
   extensibility of the schemas - it is only possible to replace or
   modify schema fragments that are factored out as named patterns.  For
   YANG this is not an issue since its 'augment' and 'refine' statements
   can delve, by using path expressions, into arbitrary depths of
   existing structures.

   In general, it not feasible to map YANG extension mechanisms to those
   of RELAX NG.  For this reason, the mapping essentially keeps the
   granularity of the original YANG data model: definitions of named
   patterns in the resulting RELAX NG schema usually have direct
   counterparts in YANG groupings and definitions of derived types.

8.4.  Handling of XML Namespaces

   Most modern XML schema languages including RELAX NG, Schematron and
   DSRL support schemas for so-called compound XML documents, which
   contain elements from multiple namespaces.  This is useful for our
   purpose since YANG-to-DSDL mapping allows for multiple input YANG
   modules that naturally leads to compound document schemas.

   RELAX NG offers two alternatives for defining the target namespaces
   in the schema:





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   1.  First possibility is the traditional XML way via the @xmlns:xxx
       attribute.

   2.  One of the target namespace URIs may be declared using the @ns
       attribute.

   In both cases, these attributes are typically attached to the <rng:
   grammar> element but may also appear elsewhere.

   The design decision for the mapping is to use exclusively the
   alternative 1, since in this case all YANG modules are represented
   symmetrically, which makes further processing of the conceptual tree
   schema considerably easier.  Moreover, this way the namespace
   prefixes declared in the input modules are recorded in the resulting
   schema - the prefix for the namespace declared using @ns would be
   lost.

   DSRL schemas can declare any number of target namespaces via the
   standard XML attributes xmlns:xxx.

   In contrast, Schematron requires all target namespaces to be defined
   in the <sch:ns> subelements of the root <sch:schema> element.

8.5.  Features and Deviations

   YANG provides statements that allow for marking parts of the schema
   as conditional ('feature' and 'if-feature' statements) or declaring
   deviations from a data model ('deviation' statement).  These
   statements are not handled by the YANG-to-DSDL mapping.  Instead, it
   is assumed that all features and deviations are specified beforehand
   and the corresponding changes in the input YANG modules are already
   applied.



















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9.  Mapping YANG Data Models to the Conceptual Tree Schema

   This section explains the main principles underlying the first step
   of the mapping.  Its result is an annotated RELAX NG schema of the
   conceptual tree, which is described in Section 8.1.

   As a special case, if the input YANG modules contain no data nodes
   (this is typical, e.g., for datatype library modules), an
   implementation MAY entirely remove the schema of the (empty)
   conceptual tree - the <rng:start> element with all its contents.  The
   output RELAX NG schema will then contain only named pattern
   definitions translated from YANG groupings and typedefs.

   Detailed specification of the mapping of individual YANG statements
   is contained in Section 11.

9.1.  Occurrence Rules for Data Nodes

   In DSDL schema languages, occurrence constraints for a node are
   always localized together with that node.  In a RELAX NG schema, for
   example, <rng:optional> pattern appears as the parent element of the
   pattern defining a leaf or non-leaf element.  Similarly, DSRL
   specifies default content separately for every single node, be it a
   leaf or non-leaf element.

   For leaf nodes in YANG modules, the occurrence constraints are also
   easily inferred from the substatements of 'leaf'.  In contrast, for a
   YANG container it is often necessary to examine its entire subtree in
   order to determine the container's occurrence constraints.

   Therefore, one of the goals of the first mapping step is to infer the
   occurrence constraints for all containers and mark accordingly the
   corresponding <rng:element> patterns in the conceptual tree schema so
   that any transformation procedure in the second mapping step can
   simply use this information and need not examine the subtree again.

   First, it has to be decided whether a given container element must
   always be present in a valid configuration.  If so, such a container
   element is called mandatory, otherwise it is called optional.  This
   constraint is closely related to the notion of mandatory nodes in
   Section 3.1 in [YANG].  The only difference is that we also consider
   list keys to be mandatory.

   The other occurrence constraint has to do with the semantics of the
   'default' statement and the possibility of removing empty non-
   presence containers.  As a result, the information set of a valid
   configuration may be modified by adding or removing certain leaf or
   container elements without changing the meaning of the configuration.



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   In this document, such elements are called implicit.

   Note that both occurrence constraints apply to containers at the top
   level of the data tree, and then also to other containers under the
   additional condition that their parent node exists in the instance
   document.  For example, consider the following YANG fragment:

       container outer {
           presence 'Presence of "outer" means something.';
           container c1 {
               leaf foo {
                   type uint8;
                   default 1;
               }
           }
           container c2 {
               leaf-list bar {
                   type uint8;
                   min-elements 0;
               }
           }
           container c3 {
               leaf baz {
                   type uint8;
                   mandatory true;
               }
           }
       }

   Here, container "outer" has the 'presence' substatement, which means
   that it is optional and not implicit.  If "outer" is not present in a
   configuration, its child containers are not present as well.
   However, if "outer" does exist, it makes sense to ask which of its
   child containers are optional and which are implicit.  In this case,
   "c1" is optional and implicit, "c2" is optional but not implicit and
   "c3" is mandatory (and therefore not implicit).

   The following subsections give precise rules for determining whether
   a container is optional or mandatory and whether it is implicit.  In
   order to simplify the recursive definition of these occurrence
   characteristics, it is useful to define them also for other types of
   data nodes, i.e., leaf, list, leaf-list and anyxml.

9.1.1.  Optional and Mandatory Nodes

   The decision whether a given node is mandatory or optional is
   governed by the following rules:




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   o  Leaf, anyxml and choice nodes are mandatory if they contain the
      substatement "mandatory true;".  For a choice node this means that
      at least one node from exactly one case branch must exist.

   o  In addition, leaf nodes are mandatory if they are declared as list
      keys.

   o  List or leaf-list nodes are mandatory if they contain 'min-
      elements' substatement with argument value greater than zero.

   o  A container node is mandatory if its definition does not contain
      the 'presence' substatement and at least one of its child nodes is
      mandatory.

   A node is optional if and only if it is not mandatory.

   In RELAX NG, definitions of nodes that are optional must be
   explicitly wrapped in the <rng:optional> element.  The mapping MUST
   use the above rules to determine whether a YANG node is optional and
   if so, insert the <rng:optional> element in the conceptual tree
   schema.

   However, alternatives in <rng:choice> are never defined as optional
   in the conceptual tree schema.  Therefore, 'anyxml', 'container',
   'leaf', 'list' and 'leaf-list' statements appearing as children of
   'choice' (so-called shorthand cases) are always mapped to mandatory
   RELAX NG patterns.  If a choice in YANG is not mandatory, <rng:
   optional> is used to wrap the entire <rng:choice> pattern.

9.1.2.  Implicit Nodes

   The following rules are used to determine whether a given node is
   implicit:

   o  List, leaf-list and anyxml nodes are never implicit.

   o  A leaf node is implicit if and only if it has a specified default
      value (either directly or via its datatype).

   o  A container node is implicit if and only if it does not have the
      'presence' substatement, none of its children is mandatory and at
      least one child is implicit.

   In the conceptual tree schema, all implicit containers, as well as
   leafs that obtain their default value from a typedef and don't have
   the @nma:default attribute, MUST be marked with @nma:implicit
   attribute having the value "true".




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   Note that Section 7.9.3 in [YANG] specifies other rules that must be
   taken into account when deciding whether a given container or leaf
   appearing inside a case of a choice is ultimately implicit or not.
   Specifically, a leaf or container under a case can be implicit only
   if the case appears in the argument of the choice's 'default'
   statement.  However, this is not sufficient by itself but also
   depends on the particular instance XML document, namely on the
   presence or absence of nodes from other (non-default) cases.  The
   details are explained in Section 10.4.

9.2.  Mapping YANG Groupings and Typedefs

   YANG groupings and typedefs are generally mapped to RELAX NG named
   patterns.  There are, however, several caveats that the mapping has
   to take into account.

   First of all, YANG typedefs and groupings may appear at all levels of
   the module hierarchy and are subject to lexical scoping, see Section
   5.5 in [YANG].  Second, top-level symbols from external modules are
   imported as qualified names represented using the external module
   namespace prefix and the name of the symbol.  In contrast, named
   patterns in RELAX NG (both local and imported via the <rng:include>
   pattern) share the same namespace and within a grammar they are
   always global - their definitions may only appear at the top level as
   children of the <rng:grammar> element.  Consequently, whenever YANG
   groupings and typedefs are mapped to RELAX NG named pattern
   definitions, their names MUST be disambiguated in order to avoid
   naming conflicts.  The mapping uses the following procedure for
   mangling the names of groupings and type definitions:

   o  Names of groupings and typedefs appearing at the top level of the
      YANG module hierarchy are prefixed with the module name and two
      underscore characters ("__").

   o  Names of other groupings and typedefs, i.e., those that do not
      appear at the top level of a YANG module, are prefixed with the
      module name, double underscore, and then the names of all ancestor
      data nodes separated by double underscore.

   o  Since the names of groupings and typedefs in YANG have different
      namespaces, an additional underline character is added to the
      beginning of the mangled names of all groupings.

   EXAMPLE.  Consider the following YANG module which imports the
   standard module "ietf-inet-types" [Ytypes]:






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   module example1 {
       namespace "http://example.com/ns/example1";
       prefix ex1;
       import "ietf-inet-types" {
           prefix "inet";
       }
       typedef vowels {
           type string {
               pattern "[aeiouy]*";
           }
       }
       grouping "grp1" {
           leaf "void" {
               type "empty";
           }
       }
       container "cont" {
           grouping "grp2" {
               leaf "address" {
                   type "inet:ip-address";
               }
           }
           leaf foo {
               type vowels;
           }
           uses "grp1";
           uses "grp2";
       }
   }

   The resulting RELAX NG schema will then contain the following named
   pattern definitions (long regular expression patterns for IPv4 and
   IPv6 addresses are not shown):


















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   <rng:define name="example1__vowels">
     <rng:data type="string">
       <rng:param name="pattern">[aeiouy]*</param>
     </rng:data>
   </rng:define>

   <rng:define name="_example1__grp1">
     <rng:optional>
       <rng:element name="ex1:void">
         <rng:empty/>
       </rng:element>
     </rng:optional>
   </rng:define>

   <rng:define name="_example1__cont__grp2">
     <rng:optional>
       <rng:element name="ex1:address">
         <rng:ref name="ietf-inet-types__ip-address"/>
       </rng:element>
     </rng:optional>
   </rng:define>

   <rng:define name="ietf-inet-types__ip-address">
     <rng:choice>
       <rng:ref name="ietf-inet-types__ipv4-address"/>
       <rng:ref name="ietf-inet-types__ipv6-address"/>
     </rng:choice>
   </rng:define>

   <rng:define name="ietf-inet-types__ipv4-address">
     <rng:data type="string">
       <rng:param name="pattern">... regex pattern ...</param>
     </rng:data>
   </rng:define>

   <rng:define name="ietf-inet-types__ipv6-address">
     <rng:data type="string">
       <rng:param name="pattern">... regex pattern ...</param>
     </rng:data>
   </rng:define>

   Note that type definitions from the "ietf-inet-types" module are
   mapped directly to the conceptual tree schema.

9.2.1.  YANG Refinements and Augments

   YANG groupings represent a similar concept as named pattern
   definitions in RELAX NG and both languages also offer mechanisms for



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   their subsequent modification.  However, in RELAX NG the definitions
   themselves are modified whereas YANG allows for modifying expansions
   of groupings.  Specifically, YANG provides two statements for this
   purpose that may appear as substatements of 'uses':

   o  'refine' statement allows for changing parameters of a schema node
      inside the grouping referenced by the parent 'uses' statement;

   o  'augment' statement can be used for adding new schema nodes to the
      grouping content.

   Both 'refine' and 'augment' statements are quite powerful in that
   they can address, using XPath-like expressions as their arguments,
   schema nodes that are arbitrarily deep inside the grouping content.
   In contrast, modifications of named pattern definitions in RELAX NG
   are applied exclusively at the topmost level of the named pattern
   content.  In order to achieve a modifiability of named patterns
   comparable to YANG, the RELAX NG schema would have to be extremely
   flat (cf. Section 8.3) and very difficult to read.

   Since the goal of the mapping described in this document is to
   generate ad hoc DSDL schemas, we decided to avoid these complications
   and instead expand the grouping and refine and/or augment it "in
   place".  In other words, every 'uses' statement which has 'refine'
   and/or 'augment' substatements is replaced by the content of the
   corresponding grouping, the changes specified in the 'refine' and
   'augment' statements are applied and the resulting YANG schema
   fragment is mapped as if the 'uses'/'grouping' indirection wasn't
   there.

   If there are further 'uses' statements inside the grouping content,
   they may require expansion, too: it is necessary if the contained
   'uses'/'grouping' pair lies on the "modification path" specified in
   the argument of a 'refine' or 'augment' statement.

   EXAMPLE.  Consider the following YANG module:















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   module example2 {
       namespace "http://example.com/ns/example2";
       prefix ex2;
       grouping leaves {
           uses fr;
           uses es;
       }
       grouping fr {
           leaf feuille {
               type string;
           }
       }
       grouping es {
           leaf hoja {
               type string;
           }
       }
       uses leaves;
   }

   The resulting conceptual tree schema contains three named pattern
   definitions corresponding to the three groupings, namely

   <rng:define name="_example2__leaves">
     <rng:ref name="_example2__fr"/>
     <rng:ref name="_example2__es"/>
   </rng:define>

   <rng:define name="_example2__fr">
     <rng:optional>
       <rng:element name="ex2:feuille">
         <rng:data type="string"/>
       </rng:element>
     </rng:optional>
   </rng:define>

   <rng:define name="_example2__es">
     <rng:optional>
       <rng:element name="ex2:hoja">
         <rng:data type="string"/>
       </rng:element>
     </rng:optional>
   </rng:define>

   and the configuration data part of the conceptual tree schema is a
   single named pattern reference:

   <rng:ref name="_example2__leaves"/>



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   Now assume that the "uses leaves" statement contains a 'refine'
   substatement, for example:

   uses leaves {
       refine "hoja" {
           default "alamo";
       }
   }

   The resulting conceptual tree schema now contains just one named
   pattern definition - "_example2__fr".  The other two groupings
   "leaves" and "es" have to be expanded because they both lie on the
   "modification path", i.e., contain the leaf "hoja" that is being
   refined.  The configuration data part of the conceptual tree schema
   now looks like this:

   <rng:ref name="_example2__fr"/>
   <rng:optional>
     <rng:element name="ex2:hoja" nma:default="alamo">
       <rng:data type="string"/>
     </rng:element>
   </rng:optional>

9.2.2.  Type Derivation Chains

   RELAX NG has no equivalent of the type derivation mechanism in YANG
   that allows to modify a built-in type (perhaps in multiple steps) by
   adding new restrictions.  When a derived YANG type is used without
   restrictions - as a substatement of either 'leaf' or another
   'typedef' - the 'type' statement is mapped simply to the <rng:ref>
   element, i.e., a named pattern reference, and the type definition is
   mapped to a RELAX NG named pattern definition.  However, if
   restrictions are specified as substatements of the 'type' statement,
   the type definition MUST be expanded at that point so that only the
   ancestor built-in type appears in the output schema, restricted with
   facets that correspond to the combination of all restrictions found
   along the type derivation chain and also in the 'type' statement.

   EXAMPLE.  Consider this YANG module:












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   module example3 {
       namespace "http://example.com/ns/example3";
       prefix ex3;
       typedef dozen {
           type uint8 {
               range 1..12;
           }
       }
       leaf month {
           type dozen;
       }

   The 'type' statement in "leaf month" is mapped simply to the
   reference <rng:ref name="example3__dozen"/> and the corresponding
   named pattern is defined as follows:

   <rng:define name="example3__dozen">
     <rng:data type="unsignedByte">
       <rng:param name="minInclusive">1</param>
       <rng:param name="maxInclusive">12</param>
     </rng:data>
   </rng:define>

   Assume now that the definition of leaf "month" is changed to

   leaf month {
       type dozen {
           range 7..max;
       }
   }

   The output RELAX NG schema then won't contain any named pattern
   definition and leaf "month" will be mapped directly to

   <rng:element name="ex3:month">
     <rng:data type="unsignedByte">
       <rng:param name="minInclusive">7</param>
       <rng:param name="maxInclusive">12</param>
     </rng:data>
   </rng:element>

   The mapping of type derivation chains may be further complicated by
   the presence of the 'default' statement in type definitions.  In the
   simple case, when a type definition containing the 'default'
   statement is used without restrictions, the 'default' statement is
   mapped to the @nma:default attribute attached to the <rng:define>
   element.




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   However, if that type definition has to be expanded, the @nma:default
   annotation arising from the expanded type or ancestor types in the
   type derivation chain MUST be attached to the element where the
   expansion occurs.  If there are multiple 'default' statements in
   consecutive steps of the type derivation, only the 'default'
   statement that is closest to the expanded type is used.

   EXAMPLE.  Consider this variation of the last example:

   module example3bis {
       namespace "http://example.com/ns/example3bis";
       prefix ex3bis;
       typedef dozen {
           type uint8 {
               range 1..12;
           }
           default 7;
       }
       leaf month {
           type dozen;
       }

   The 'typedef' statement in this module is mapped to the following
   named pattern definition:

   <rng:define name="example3bis__dozen" @nma:default="7">
     <rng:data type="unsignedByte">
       <rng:param name="minInclusive">1</param>
       <rng:param name="maxInclusive">12</param>
     </rng:data>
   </rng:define>

   If the "dozen" type is restricted when used in the leaf "month"
   definition as in the previous example, the "dozen" type has to be
   expanded and @nma:default becomes an attribute of the <ex3bis:month>
   element definition:

   <rng:element name="ex3bis:month" @nma:default="7">
     <rng:data type="unsignedByte">
       <rng:param name="minInclusive">7</param>
       <rng:param name="maxInclusive">12</param>
     </rng:data>
   </rng:element>

   However, if the definition of leaf "month" itself contained the
   'default' substatement, the default specified for the "dozen" type
   will be ignored.




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9.3.  Translation of XPath Expressions

   YANG uses full XPath 1.0 syntax [XPath] for the arguments of 'must',
   'when' and 'path' statements.  As the names of data nodes defined in
   a YANG module always belong to the namespace of that YANG module,
   YANG adopted a simplification similar to the concept of default
   namespace in XPath 2.0: node names needn't carry a namespace prefix
   inside the module where they are defined and the local module's
   namespace is assumed.

   If an XPath expression is carried over to a NETMOD-specific
   annotation in the conceptual tree schema, it MUST be translated into
   a fully conformant XPath 1.0 expression that also reflects the
   hierarchy of the conceptual data tree:

   1.  Each unprefixed node name MUST be prepended with the local
       module's namespace prefix declared by the 'prefix' statement.

   2.  Absolute XPath expressions, i.e., those starting with a slash,
       MUST be prepended with appropriate path in the conceptual tree,
       according to the YANG specification of context for XPath
       expressions, see [YANG], Sections 7.5.3 and 7.19.5.

   Translation rule 2 means for example that absolute XPath expressions
   appearing in the main configuration data tree always start with "nmt:
   netmod-tree/nmt:top/", those appearing in a notification always start
   with "nmt:netmod-tree/nmt:notifications/nmt:notification/", etc.

   EXAMPLE.  YANG XPath expression "/dhcp/max-lease-time" appearing in
   the main configuration data will be translated to "nmt:netmod-tree/
   nmt:top/dhcp:dhcp/dhcp:max-lease-time".

   The key identifiers and "descendant schema node identifiers" (see the
   ABNF production for and "descendant-schema-nodeid" in Section 12 of
   [YANG]) are not XPath expressions but SHOULD be translated by adding
   local module prefixes as well.

9.4.  YANG Language Extensions

   YANG allows for extending its own language in-line by adding new
   statements with keywords from special namespaces.  Such extensions
   first have to be declared using the 'extension' statement and then
   can be used as the standard YANG statements, from which they are
   distinguished by a namespace prefix qualifying the extension keyword.
   RELAX NG has a similar extension mechanism - XML elements and
   attributes with names from foreign namespaces may be inserted at
   almost any place of a RELAX NG schema.




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   YANG language extensions may or may not have a meaning in the context
   of DSDL schemas.  Therefore, an implementation MAY ignore any or all
   of the extensions.  However, an extension that is not ignored MUST be
   mapped to XML element(s) and/or attribute(s) that exactly match the
   YIN form of the extension, see Section 11.1 in [YANG].

   EXAMPLE.  Consider the following extension defined by the "acme"
   module:

   extension documentation-flag {
       argument number;
   }

   This extension can then be used in the same or another module, for
   instance like this:

   leaf folio {
       acme:documentation-flag 42;
       type string;
   }

   If this extension is honored by the mapping, it will be mapped to

   <rng:element name="acme:folio">
      <acme:documentation-flag number="42"/>
      <rng:data type="string"/>
   </rng:element>

   Note that the 'extension' statement itself is not mapped in any way.






















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10.  Mapping Conceptual Tree Schema to DSDL

   As explained in Section 6, the second step of the YANG-to-DSDL
   mapping takes the conceptual tree schema and transforms it to various
   DSDL schemas prepared for validating instance XML documents.  As an
   input parameter, this step takes in the simplest case just a
   specification of the NETCONF XML document type (or combination of
   multiple types) that is to be validated.  These document type can be,
   for example, the content of a datastore, reply to <nc:get> or <nc:
   get-config>, other RPC requests or replies and notifications.

   In general, the second mapping step has to accomplish the following
   three tasks:

   1.  Extract the part(s) of the conceptual tree schema that are
       appropriate for the requested document type.  For example, if a
       <get> reply is to be validated, the subtree under <nmt:top> must
       be selected.

   2.  The schema must be adapted to the specific encapsulating XML
       elements mandated by the RPC layer.  These are, for example, <nc:
       rpc> and <nc:data> elements in the case of a <get> reply or <en:
       notification> for a notification.

   3.  Finally, NETMOD-specific annotations that are relevant for the
       schema language of the generated schema must be mapped to the
       corresponding rules.

   These three tasks are together much simpler than the first mapping
   step and can be effectively implemented using XSL transformations
   [XSLT].

   The following subsections describe the details of the second mapping
   step for the individual DSDL schema languages.  Section 12 then
   contains a detailed specification for the mapping of all NETMOD-
   specific annotations.

10.1.  Generating RELAX NG Schemas for Various Document Types

   With one minor exception, obtaining a validating RELAX NG schema from
   the conceptual tree schema really means only taking appropriate parts
   of the conceptual tree schema and assembling them in a new RELAX NG
   grammar, perhaps after removing all unwanted annotations.  Depending
   on the XML document type that is the target for validation (<get>/
   <get-config> reply, RPC or notification) a corresponding top-level
   part of the grammar MUST be added as described in the following
   subsections.




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   Schemas for multiple alternative target document types can also be
   easily generated by enclosing the definitions for requested type in
   <rng:choice> element.

   In order to avoid copying common named pattern definitions to every
   single output RELAX NG file, these schema-independent definitions
   SHOULD be collected in a library file which is then included by the
   validating RELAX NG schemas.  Appendix B has the listing of this
   library file.

   The minor exception mentioned above is the annotation @nma:config,
   which must be observed if the target document type is <get-config>
   reply.  In this case, each element definition that has this attribute
   with the value "false" MUST be removed from the schema together with
   its descendants.  See Section 12.1 for more details.

10.1.1.  Reply to <get> or <get-config>

   For a reply to <get> or <get-config>, the mapping must take the part
   of the conceptual tree schema under the definition of <nmt:top> and
   insert it in the following grammar:

   <rng:grammar ... namespaces etc. ...>
     <rng:include href="relaxng-lib.rng"/>
     <rng:start>
       <rng:element name="nc:rpc-reply">
         <rng:ref name="message-id-attribute"/>
         <rng:element name="nc:data">
           ... patterns defining contents of "nmt:top" subtree ...
         </rng:element>
       </rng:element>
     </rng:start>
     ... named pattern definitions ...
   </rng:grammar>

   The definition for the named pattern "message-id-attribute" is found
   in the library file "relaxng-lib.rng" which is included on the second
   line (see Appendix B).

   Definitions of other named patterns MUST be copied literally from the
   conceptual tree schema to the resulting grammar.  However, an
   implementation MAY choose to copy only those definitions that are
   really used in the particular output grammar.

10.1.2.  Remote Procedure Calls

   For an RPC method named "myrpc" and defined in a YANG module with
   prefix "yam", the corresponding schema subtree is identified by the



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   definition of <nmt:rpc-method> element whose <nmt:input> subelement
   has <yam:myrpc> as the only child.

   The mapping must also take into account whether the target document
   type is an RPC request or reply.  For "yam:myrpc" request, the
   resulting grammar looks as follows:

   <rng:grammar ... namespaces etc. ...>
     <rng:include href="relaxng-lib.rng"/>
     <rng:start>
       <rng:element name="nc:rpc">
         <rng:ref name="message-id-attribute"/>
         <rng:element name="yam:myrpc">
           ... patterns defining contents of the subtree ...
           ... "nmt:rpc-method/nmt:input/yam:myrpc" ...
         </rng:element>
       </rng:element>
     </rng:start>
     ... named pattern definitions ...
   </rng:grammar>

   For "yam:myrpc" reply, the output grammar is

   <rng:grammar ... namespaces etc. ...>
     <rng:include href="relaxng-lib.rng"/>
     <rng:start>
       <rng:element name="nc:rpc-reply">
         <rng:ref name="message-id-attribute"/>
         ... patterns defining contents of the corresponding ...
         ... "nmt:rpc-method/nmt:output" subtree ...
       </rng:element>
     </rng:start>
     ... named pattern definitions ...
   </rng:grammar>

   In both cases, exact copies of named pattern definitions from the
   conceptual tree schema MUST be inserted, but an implementation MAY
   choose to include only those used for the given RPC.

10.1.3.  Notifications

   For a notification named "mynotif" and defined in a YANG module with
   prefix "yam", the corresponding schema subtree is identified by the
   definition of <nmt:notification> element that has the single child
   <yam:mynotif>.

   The resulting grammar looks as follows:




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   <rng:grammar ... namespaces etc. ...>
     <rng:include href="relaxng-lib.rng"/>
     <rng:start>
       <rng:element name="en:notification">
         <rng:ref name="eventTime-element"/>
         <rng:element name="yam:mynotif">
           <!-- patterns defining contents of
                "nmt:rpc-notification/yam:mynotif" subtree -->
         </rng:element>
       </rng:element>
     </rng:start>
     <!-- named pattern definitions -->
   </rng:grammar>

   The definition of the named pattern "eventTime-element" is found in
   the "relaxng-lib.rng" library file, see Appendix B.

   Again, exact copies of named pattern definitions from the conceptual
   tree schema MUST be inserted, but an implementation MAY choose to
   include only those used for the given notification.

10.2.  Mapping Semantic Constraints to Schematron

   Schematron schemas tend to be much flatter and more uniform compared
   to RELAX NG.  They have exactly four levels of XML hierarchy: <sch:
   schema>, <sch:pattern>, <sch:rule> and <sch:assert> or <sch:report>.

   In a Schematron schema generated by the second mapping step, the
   basic unit of organization is a rule represented by the <sch:rule>
   element.  Every rule corresponds to exactly one element definition
   pattern in the conceptual tree schema:

   <sch:rule context="XELEM">
     ...
   </sch:rule>

   The value of the mandatory @context attribute of <sch:rule> (denoted
   as XELEM) MUST be set to the absolute path of the context element in
   the data tree.  The <sch:rule> element contains the mappings of one
   or more of the following NETMOD-specific annotations, if they are
   attached to the context element: <nma:instance-identifier>, @nma:key,
   @nma:leafref, @nma:min-elements, @nma:max-elements, <nma:must>, @nma:
   unique and <nma:when>.

   In the opposite direction, however, not every element definition
   pattern in the conceptual tree schema has a corresponding rule in the
   Schematron schema: definitions of elements the carry none of the
   above annotations are omitted.



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   Schematron rules may be further grouped into patterns represented by
   the <sch:pattern> element.  The mapping uses patterns only for
   discriminating between subsets of rules that belong to different
   validation phases, see Section 10.2.1.  Therefore, the <sch:schema>
   always has exactly two <sch:pattern> children: one named "standard"
   contains rules for all annotations except <nma:instance-identifier>
   and @nma:leafref, and another named "ref-integrity" containing rules
   for these two remaining annotations, i.e., referential integrity
   checks.

   Element definitions in the conceptual tree schema that appear inside
   a named pattern definition (i.e., have <rng:define> among its
   ancestors) are subject to a different treatment.  This is because
   their path in the data tree is not fixed - the named pattern may be
   referred to in multiple places.  The mapping uses Schematron abstract
   rules to handle this case: An element definition inside a named
   pattern is mapped to an abstract rule and every use of the named
   pattern then extends (uses) this abstract rule in the concrete
   context.

   EXAMPLE.  Consider this element pattern annotated with <nma:must>:

   <rng:element name="dhcp:default-lease-time">
     <rng:data type="unsignedInt"/>
     <nma:must assert=". &lt;= ../dhcp:max-lease-time">
       <nma:error-message>
         The default-lease-time must be less than max-lease-time
       </nma:error-message>
     </nma:must>
   </rng:element>

   If this element pattern appears outside any named pattern and as a
   child of <dhcp:dhcp> (as it does in the DHCP schema, see
   Appendix C.2), it is mapped to the following Schematron rule:

   <sch:rule context="/nc:rpc-reply/nc:data/dhcp:dhcp/
                     dhcp:default-lease-time">
     <sch:assert test=". &lt;= ../dhcp:max-lease-time">
       The default-lease-time must be less than max-lease-time
     </sch:assert>
   </sch:rule>

   Now assume the element definition is inside a named pattern
   definition, say







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   <rng:define name="_dhcp__default-lease-time">
     <rng:element name="dhcp:default-lease-time">
       ... same content ...
     </rng:element>
   </rng:define>

   In this case it is mapped to an abstract rule, for instance

   <sch:rule id="id31415926" abstract="true">
     <sch:assert test=". &lt;= ../dhcp:max-lease-time">
       The default-lease-time must be less than max-lease-time
     </sch:assert>
   </sch:rule>

   Any use of the named pattern definition via <rng:ref
   name="_dhcp__default-lease-time"/> then results in a new rule
   extending the abstract one, for example

   <sch:rule context="/nc:rpc-reply/nc:data/dhcp:dhcp/
                     dhcp:default-lease-time">
     <sch:extends rule="id31415926"/>
   </sch:rule>

   Care must be taken that the value of the @context attribute in
   general consists of two parts in this case: its beginning is
   determined by the location of the <rng:ref> element in the main
   schema tree and the rest of the path comes from the relative position
   of the annotated element definition inside the named pattern.  The
   situation becomes even more complex when the mapping has to deal with
   chained definitions of named patterns (<rng:ref> inside <rng:
   define>).  The @context value then must be recursively glued together
   from multiple parts.

   The mapping from the conceptual tree schema to Schematron proceeds in
   the following steps:

   1.  First, the active subtree(s) of the conceptual tree schema must
       be selected depending on the requested target document type.
       This procedure is identical to the RELAX NG case, including the
       handling of @nma:config if the target document type is <get-
       config> reply.

   2.  Namespaces of all input YANG modules, together with the
       namespaces of base NETCONF ("nc" prefix) or notifications ("en"
       prefix) MUST be declared using the <sch:ns> element, for example

      <sch:ns uri="http://example.com/ns/dhcp" prefix="dhcp"/>




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   3.  Validation phases are defined (see Section 10.2.1) and their
       constituting patterns "standard" and "ref-integrity" created.

   4.  For either validation phase, the input conceptual tree schema is
       scanned and element definitions with annotations relevant for the
       given phase are selected and a <sch:rule> is created for each of
       them.  As explained above, the rule is abstract if the element
       definition appears inside a named pattern.

   5.  All annotations attached to the given element definition are then
       mapped using the mapping rules specified in Section 12.  The
       resulting <sch:assert> or <sch:report> elements are the installed
       as children of the <sch:rule> element.

10.2.1.  Validation Phases

   In certain situations it is useful to validate XML instance documents
   without enforcing the referential integrity constraints represented
   by the @nma:leafref and <nma:instance-identifier> annotations.  For
   example, a candidate configuration referring to configuration
   parameters or state data of certain hardware will not pass full
   validation before the hardware is installed.  To handle this, the
   Schematron mapping introduces two validation phases:

   o  Validation phase "full", which is the default, checks all semantic
      constraints.

   o  Validation phase "noref" is the same as "full" except it doesn't
      check referential integrity constraints.

   A parameter identifying the validation phase to use has to be passed
   to the Schematron processor or otherwise "full" phase is assumed by
   default.  How this is exactly done depends on the concrete Schematron
   processor and is outside the scope of this document.

   The validation phases are defined in Schematron by listing the
   patterns that are to be applied for each phase.  Therefore, the
   mapping puts the rules for referential integrity checking to a
   special <sch:pattern> with @id attribute set to "ref-integrity".  The
   rules mapped from the remaining semantic constraints are put to
   another <sch:pattern> with @id attributes set to "standard".

   With validation phases, the resulting Schematron schema has the
   following overall structure:







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   <sch:schema xmlns:sch="http://purl.oclc.org/dsdl/schematron">
     <sch:ns uri="..." prefix="..."/>
     ... more NS declarations ...
     <sch:phase id="full">
       <sch:active pattern="standard"/>
       <sch:active pattern="ref-integrity"/>
     </sch:phase>
     <sch:phase id="noref">
       <sch:active pattern="standard"/>
     </sch:phase>
     <sch:pattern id="standard">
       ... all rules except ref. integrity checks ...
     </sch:pattern>
     <sch:pattern id="ref-integrity">
       ... rules for ref. integrity checks ...
     </sch:pattern>
   </sch:schema>

10.3.  Constraints on Mandatory Choice

   In order to fully represent the semantics of YANG 'choice' statement
   with "mandatory true;" substatement, the RELAX NG grammar has to be
   combined with a special Schematron rule.

   EXAMPLE.  Consider the following module:

   module example4 {
       namespace "http://example.com/ns/example4";
       prefix ex4;
       choice foobar {
           mandatory true;
           case foo {
               leaf foo1 {
                   type uint8;
               }
               leaf foo2 {
                   type uint8;
               }
           }
           leaf bar {
               type uint8;
           }
       }
   }

   In this module, all three leaf nodes in both case branches are
   optional but because of the "mandatory true;" statement, at least one
   of them must be present in a valid configuration.  The 'choice'



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   statement from this module is mapped to the following fragment of the
   conceptual tree schema:

   <rng:choice>
     <rng:interleave>
       <rng:optional>
         <rng:element name="ex4:foo1">
           <rng:data type="unsignedByte"/>
         </rng:element>
       </rng:optional>
       <rng:optional>
         <rng:element name="ex4:foo2">
           <rng:data type="unsignedByte"/>
         </rng:element>
       </rng:optional>
     </rng:interleave>
     <rng:element name="ex4:bar">
       <rng:data type="unsignedByte"/>
     </rng:element>
   </rng:choice>

   In the second case branch, the "ex4:bar" element is defined as
   mandatory so that this element must be present in a valid
   configuration if this branch is selected.  However, the two elements
   in the first branch "foo" cannot be both declared as mandatory since
   each of them alone suffices for a valid configuration.  As a result,
   the above RELAX NG fragment would successfully validate
   configurations where none of the three leaf elements is present.

   Therefore, mandatory choices, which can be recognized in the
   conceptual tree schema as <rng:choice> elements that do not have
   <optional> as their parent, have to be handled in a special way: For
   each mandatory choice where at least one of the cases contains more
   than one node, a rule MUST be present in the "standard" pattern of
   the Schematron schema enforcing the presence of at least one element
   from any of the cases.  (RELAX NG schema guarantees that elements
   from different cases cannot be mixed together, that all mandatory
   nodes are present etc.).

   For the example module above, the Schematron rule will be as follows:

   <sch:rule context="/nc:rpc-reply/nc:data">
     <sch:assert test="ex4:foo1 or ex4:foo2 or ex4:bar">
       Node(s) from at least one case of choice "foobar" must exist.
     </sch:assert>
   </sch:rule>





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10.4.  Mapping Default Values to DSRL

   DSRL is the only component of DSDL that is allowed to change the
   information set of the validated XML document.  While DSRL also has
   other functions, YANG-to-DSDL mapping uses it only for specifying and
   applying default content.  For XML instance documents based on YANG
   data models, insertion of default content may potentially take place
   for all implicit nodes defined by the rules in Section 9.1.2.

   In DSRL, the default content of an element is specified using the
   <dsrl:default-content> element, which is a child of <dsrl:element-
   map>.  Two sibling elements of <dsrl:default-content> determine the
   context for application of the default content, see [DSRL]:

   o  <dsrl:parent> element contains an XSLT pattern specifying the
      parent element; the default content is applied only if the parent
      element exists in the instance document.

   o  <dsrl:name> contains the XML name of the element which, if missing
      or empty, is inserted together with the content of <dsrl:default-
      content>.

   The <dsrl:parent> element is optional in a general DSRL schema but
   for the purpose of the YANG-to-DSDL mapping this element MUST be
   always present in order to guarantee proper application of default
   content.

   DSRL mapping only deals with element patterns defining implicit nodes
   (see Section 9.1.2).  In the conceptual tree schema, such element
   patterns are distinguished by having NETMOD-specific annotation
   attributes @nma:default or @nma:implicit, i.e., either

   <rng:element name="ELEM" nma:default="DEFVALUE">
     ...
   </rng:element>

   or

   <rng:element name="ELEM" nma:implicit="true">
     ...
   </rng:element>

   The former case applies to leaf nodes having the 'default'
   substatement, but also to leaf nodes that obtain their default value
   from a typedef, if this typedef is expanded according to the rules in
   Section 9.2.2 so that the @nma:default annotation is attached
   directly to the leaf's element pattern.




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   The latter case is used for all implicit containers (see Section 9.1)
   and for leafs that obtain the default value from a typedef and don't
   have the @nma:default annotation.

   In the simplest case, both element patterns are mapped to the
   following DSRL element map:

   <dsrl:element-map>
     <dsrl:parent>XPARENT</dsrl:parent>
     <dsrl:name>ELEM</dsrl:name>
     <dsrl:default-content>DEFCONT</dsrl:default-content>
     </dsrl:element-map>

   where XPARENT is the absolute XPath of ELEM's parent element in the
   data tree and DEFCONT is constructed as follows:

   o  If the implicit node ELEM is a leaf and has the @nma:default
      attribute, DEFCONT is set to the value of this attribute (denoted
      above as DEFVALUE).

   o  If the implicit node ELEM is a leaf and has the @nma:implicit
      attribute with the value "true", the default value has to be
      determined from the @nma:default attribute of the definition of
      ELEM's type (perhaps recursively) and used in place of DEFCONT in
      the above DSRL element map.  See also Section 9.2.2.

   o  Otherwise, the implicit node ELEM is a container and DEFCONT is
      constructed as an XML fragment containing all descendant elements
      of ELEM that have either @nma:implicit or @nma:default attribute.

   The <rng:element>, <rng:group> or <rng:interleave>patterns appearing
   directly under <rng:choice> MUST NOT have either @nma:default or
   @nma:implicit annotation unless they belong to the default case of a
   YANG choice (see Section 11.12).

   In addition, when mapping the default case of a choice, it has to be
   guaranteed that the default content is not applied if any node from
   any non-default case is present.  This is accomplished by setting
   <dsrl:parent> in a special way:

   <dsrl:parent>XPARENT[not (ELEM1|ELEM2|...|ELEMn)]</dsrl:parent>

   where ELEM1, ELEM2, ...  ELEMn are the names of all top-level nodes
   from all non-default cases.  The rest of the element map is exactly
   as before.

   EXAMPLE.  Consider the following YANG module:




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   module example5 {
     namespace "http://example.com/ns/example5";
     prefix ex5;
     container outer {
       leaf leaf1 {
         type uint8;
         default 1;
       }
       choice one-or-two {
         default "one";
         container one {
           leaf leaf2 {
             type uint8;
             default 2;
           }
         }
         leaf leaf3 {
           type uint8;
           default 3;
         }
       }
     }
   }

   The DSRL schema generated for the "get-reply" target document type
   will be:

























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  <dsrl:maps xmlns:dsrl="http://purl.oclc.org/dsdl/dsrl"
             xmlns:ex5="http://example.com/ns/example5"
             xmlns:nc="urn:ietf:params:xml:ns:netconf:base:1.0">
    <dsrl:element-map>
      <dsrl:parent>/nc:rpc-reply/nc:data</dsrl:parent>
      <dsrl:name>ex5:outer</dsrl:name>
      <dsrl:default-content>
        <ex5:leaf1>1</ex5:leaf1>
        <ex5:one><ex5:leaf2>2</ex5:leaf2></ex5:one>
      </dsrl:default-content>
    </dsrl:element-map>
    <dsrl:element-map>
      <dsrl:parent>
        /nc:rpc-reply/nc:data/ex5:outer[not(ex5:leaf3)]
      </dsrl:parent>
      <dsrl:name>ex5:one</dsrl:name>
      <dsrl:default-content>
        <ex5:leaf2>2</ex5:leaf2>
      </dsrl:default-content>
    </dsrl:element-map>
    <dsrl:element-map>
      <dsrl:parent>/nc:rpc-reply/nc:data/ex5:outer</dsrl:parent>
      <dsrl:name>ex5:leaf1</dsrl:name>
      <dsrl:default-content>1</dsrl:default-content>
    </dsrl:element-map>
    <dsrl:element-map>
      <dsrl:parent>/nc:rpc-reply/nc:data/ex5:outer</dsrl:parent>
      <dsrl:name>ex5:one</dsrl:name>
      <dsrl:default-content>
        <ex5:leaf2>2</ex5:leaf2>
      </dsrl:default-content>
    </dsrl:element-map>
    <dsrl:element-map>
      <dsrl:parent>/nc:rpc-reply/nc:data/ex5:outer/ex5:one</dsrl:parent>
      <dsrl:name>ex5:leaf2</dsrl:name>
      <dsrl:default-content>2</dsrl:default-content>
    </dsrl:element-map>
  </dsrl:maps>

   Note that the default value for "leaf3" defined in the YANG module is
   ignored because "leaf3" represents a non-default alternative of a
   choice and as such never becomes an implicit element.









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11.  Mapping YANG Statements to Conceptual Tree Schema

   Each subsection in this section is devoted to one YANG statement and
   provides the specification how the statement is mapped to the
   annotated RELAX NG schema of the conceptual tree.  This is the first
   step of the mapping procedure as explained in Section 6.  The
   subsections are sorted alphabetically by the statement keyword.

   Each YANG statement is mapped to an XML fragment, typically a single
   element or attribute but it may also be a larger structure.  The
   mapping procedure is inherently recursive, which means that after
   finishing a statement the mapping continues with its substatements,
   if there are any, and a certain element of the resulting fragment
   becomes the parent of other fragments resulting from the mapping of
   substatements.  Any changes to this default recursive procedure are
   explicitly specified.

   YANG XML encoding rules translate to the following rules for ordering
   multiple subelements:

   1.  Within the <nmt:rpc-methods> subtree (i.e., for RPC input and
       output parameters) the order of subelements is fixed and their
       definitions in the conceptual tree schema MUST follow the order
       specified in the source YANG module.

   2.  When mapping the 'list' statement, all keys MUST come before any
       other subelements and in the same order as they are declared in
       the 'key' statement.  The order of the remaining (non-key)
       subelements is not specified, so their definitions in the
       conceptual tree schema MUST be enclosed in the <rng:interleave>
       element.

   3.  Otherwise, all definitions of subelements in the conceptual tree
       schema MUST be enclosed in the <rng:interleave> element.

   We use the following conventions:

   o  The argument of the statement being mapped is denoted by ARGUMENT.

   o  The element in the RELAX NG schema that becomes the parent of the
      resulting XML fragment is denoted by PARENT.

11.1.  The anyxml Statement

   This statement is mapped to <rng:element> element and ARGUMENT with
   prepended local namespace prefix becomes the value of its @name
   attribute.  The content of <rng:element> is




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   <rng:ref name="__anyxml__"/>

   Substatements of the 'anyxml' statement, if any, MAY be mapped to
   additional children of the RELAX NG element definition.

   If the 'anyxml' statement occurs in any of the input YANG modules,
   the following pattern definition MUST be added exactly once to the
   RELAX NG schema as a child of the <rng:grammar> element (cf. [Vli04],
   p. 172):

   <rng:define name="__anyxml__">
     <rng:zeroOrMore>
       <rng:choice>
         <rng:attribute>
           <rng:anyName/>
         </rng:attribute>
         <rng:element>
           <rng:anyName/>
           <rng:ref name="__anyxml__"/>
         </rng:element>
         <rng:text/>
       </rng:choice>
     </rng:zeroOrMore>
   </rng:define>

   EXAMPLE: YANG statement in a module with namespace prefix "yam"

   anyxml data {
       description "Any XML content allowed here.";
   }

   is mapped to the following fragment:

   <rng:element name="yam:data">
       <a:documentation>Any XML content allowed here</a:documentation>
       <rng:ref name="__anyxml__"/>
   </rng:element>

   An anyxml node is optional if there is no "mandatory true;"
   substatement.  The <rng:element> element then MUST be wrapped in
   <rng:optional>, except when the 'anyxml' statement is a child of the
   'choice' statement and thus forms a shorthand case for that choice
   (see Section 9.1.1 for details).

11.2.  The argument Statement

   This statement is not mapped to the output schema, but see the rules
   for handling extensions in Section 9.4.



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11.3.  The augment Statement

   As a substatement of 'uses', this statement is handled as a part of
   'uses' mapping, see Section 11.57.

   At the top level of a module or submodule, the 'augment' statement is
   used for augmenting the schema tree of another YANG module.  If the
   latter module is not processed within the same mapping session, the
   top-level 'augment' statement MUST be ignored.  Otherwise, the
   contents of the statement are added to the foreign module with the
   namespace of the module where the 'augment' statement appears.

11.4.  The base Statement

   This statement is ignored as a substatement of 'identity' and handled
   within the 'identityref' type if it appears as a substatement of that
   type definition, see Section 11.53.5.

11.5.  The belongs-to Statement

   This statement is not used since processing of submodules is always
   initiated from the main module, see Section 11.24.

11.6.  The bit Statement

   This statement is handled within the "bits" type, see
   Section 11.53.3.

11.7.  The case Statement

   This statement is mapped to <rng:group> or <rng:interleave> element,
   depending on whether the statement belongs to an RPC definition or
   not.  If the argument of a sibling 'default' statement equals to
   ARGUMENT, @nma:implicit attribute with the value "true" MUST be added
   to that <rng:group> or <rng:interleave> element.  The @nma:implicit
   attribute MUST NOT be used for nodes at the top-level of a non-
   default case (see Section 7.9.3 in [YANG]).

11.8.  The choice Statement

   This statement is mapped to <rng:choice> element.

   Unless 'choice' has the 'mandatory' substatement with the value
   "true", the <rng:choice> element MUST be wrapped in <rng:optional>.
   The 'choice' statement with "mandatory true;" may require additional
   handling, see Section 10.3.

   The alternatives in <rng:choice> - mapped from either the 'case'



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   statement or a shorthand case - MUST NOT be defined as optional.

11.9.  The config Statement

   This statement is mapped to @nma:config attribute and ARGUMENT
   becomes its value.

11.10.  The contact Statement

   This statement SHOULD NOT be used by the mapping since the output
   RELAX NG schema may result from multiple YANG modules created by
   different authors.  The schema contains references to all input
   modules in the Dublin Core elements <dc:source>, see Section 11.34.
   The original YANG modules are the authoritative sources of the
   authorship information.

11.11.  The container Statement

   Using the rules specified in Section 9.1.1, the mapping algorithm
   MUST determine whether the statement defines an optional container,
   and if so, insert the <rng:optional> element and make it the new
   PARENT.

   The container defined by this statement is then mapped to the <rng:
   element> element, which becomes a child of PARENT and uses ARGUMENT
   with prepended local namespace prefix as the value of its @name
   attribute.

   Finally, using the rules specified in Section 9.1.2, the mapping
   algorithm MUST determine whether the container is implicit, and if
   so, add the attribute @nma:implicit with the value "true" to the
   <rng:element> element.

11.12.  The default Statement

   If this statement is a substatement of 'leaf', it is mapped to the
   @nma:default attribute of PARENT and ARGUMENT becomes its value.

   As a substatement of 'typedef', the 'default' statement is also
   mapped to the @nma:default attribute with the value of ARGUMENT.  The
   placement of this attribute depends on whether or not the type
   definition has to be expanded when it is used:

   o  If the type definition is not expanded, @nma:default becomes an
      attribute of the <rng:define> pattern resulting from the parent
      'typedef' mapping.





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   o  Otherwise, @nma:default becomes an attribute of the ancestor RELAX
      NG pattern inside which the expansion takes place.

   Details and an example are given in Section 9.2.2.

   Finally, as a substatement of 'choice', the 'default' statement
   identifies the default case and is handled within the 'case'
   statement, see Section 11.7.  If the default case uses the shorthand
   notation where the 'case' statement is omitted, the @nma:implicit
   attribute with the value "true" is either attached to the node
   representing the default case in the shorthand notation or,
   alternatively, an extra <rng:group> element MAY be inserted and the
   @nma:implicit attribute attached to it.  In the latter case, the net
   result is the same as if the 'case' statement wasn't omitted for the
   default case.

   EXAMPLE.  The following 'choice' statement in a module with namespace
   prefix "yam"

   choice leaves {
       default feuille;
       leaf feuille { type empty; }
       leaf hoja { type empty; }
   }

   is either mapped directly to

   <rng:choice>
     <rng:element name="yam:feuille" nma:implicit="true">
       <rng:empty/>
     </rng:element>
     <rng:element name="yam:hoja">
       <rng:empty/>
     </rng:element/>
   </rng:choice>

   or the default case may be wrapped in an extra <rng:group>:

   <rng:choice>
     <rng:group nma:implicit="true">
       <rng:element name="yam:feuille">
         <rng:empty/>
       </rng:element>
     </rng:group>
     <rng:element name="yam:hoja">
       <rng:empty/>
     </rng:element/>
   </rng:choice>



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11.13.  The description Statement

   This statement MAY be ignored.  Otherwise, it is mapped to the DTD
   compatibility element <a:documentation> and ARGUMENT becomes its
   text.

   In order to get properly formatted in the RELAX NG compact syntax,
   this element SHOULD be inserted as the first child of PARENT.

11.14.  The deviation Statement

   This statement is ignored, see Section 8.5.

11.15.  The enum Statement

   This statement is mapped to <rng:value> element and ARGUMENT becomes
   its text.  All substatements except 'status' are ignored because the
   <rng:value> element cannot contain annotation elements, see [RNG],
   section 6.

11.16.  The error-app-tag Statement

   This statement is ignored unless it is a substatement of 'must'.  In
   the latter case it is mapped to the <nma:error-app-tag> element.  See
   also Section 11.35.

11.17.  The error-message Statement

   This statement is ignored unless it is a substatement of 'must'.  In
   the latter case it is mapped to the <nma:error-message> element.  See
   also Section 11.35.

11.18.  The extension Statement

   This statement is ignored.  However, extensions to the YANG language
   MAY be mapped as described in Section 9.4.

11.19.  The feature Statement

   This statement is ignored, see Section 8.5.

11.20.  The grouping Statement

   This statement is mapped to a RELAX NG named pattern definition <rng:
   define>, but only if the grouping defined by this statement is used
   without refinements and augments in at least one of the input
   modules.  In this case, the named pattern definition becomes a child
   of the <rng:grammar> element and its name is ARGUMENT mangled



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   according to the rules specified in Section 9.2.

   Whenever a grouping is used with additional refinements and/or
   augments, the grouping is expanded so that the refinements and
   augments may be applied in place to the prescribed schema nodes.  See
   Section 9.2.1 for further details and an example.

   An implementation MAY offer the option of recording all 'grouping'
   statements as named patterns in the output RELAX NG schema even if
   they are not referenced.  This is useful for mapping YANG "library"
   modules containing only 'typedef' and/or 'grouping' statements.

11.21.  The identity Statement

   This statement is not specifically mapped.  However, if the identity
   defined by this statement is used as the base for an "identityref"
   type in any of the input modules, or is derived from this base,
   ARGUMENT will appear as the text of one of the <rng:value> elements
   in the mapping of that "identityref" type.  See Section 11.53.5 for
   more details and an example.

11.22.  The if-feature Statement

   This statement is ignored, see Section 8.5.

11.23.  The import Statement

   This statement is not specifically mapped.  The module whose name is
   in ARGUMENT has to be parsed so that the importing module be able to
   use its top-level groupings and typedefs and also augment the data
   tree of the imported module.

   If the 'import' statement has the 'revision' substatement, the
   corresponding revision of the imported module MUST be used.  The
   mechanism for finding a given module revision is outside the scope of
   this document.

11.24.  The include Statement

   This statement is not specifically mapped.  The submodule whose name
   is in ARGUMENT has to be parsed and its contents mapped exactly as if
   the submodule text was a subset of the main module text.

   If the 'include' statement has the 'revision' substatement, the
   corresponding revision of the submodule MUST be used.  The mechanism
   for finding a given submodule revision is outside the scope of this
   document.




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11.25.  The input Statement

   This statement is handled within 'rpc' statement, see Section 11.50.

11.26.  The key Statement

   This statement is mapped to @nma:key attribute.  ARGUMENT MUST be
   translated so that every key is prefixed with the namespace prefix of
   the local module.  The result of this translation then becomes the
   value of the @nma:key attribute.

11.27.  The leaf Statement

   This statement is mapped to the <rng:element> element and ARGUMENT
   with prepended local namespace prefix becomes the value of its @name
   attribute.

   A leaf is optional if there is no "mandatory true;" substatement and
   if the leaf is not declared among the keys of an enclosing list.  The
   <rng:element> element then MUST be wrapped in <rng:optional>, except
   when the 'leaf' statement is a child of the 'choice' statement and
   thus forms a shorthand case for that choice (see Section 9.1.1 for
   details).

11.28.  The leaf-list Statement

   This statement is mapped to a block enclosed by either <rng:
   zeroOrMore> or <rng:oneOrMore> element depending on whether the
   argument of 'min-elements' substatement is "0" or positive,
   respectively (it is zero by default).  This <rng:zeroOrMore> or <rng:
   oneOrMore> element becomes the PARENT.

   <rng:element> is then added as a child element of PARENT and ARGUMENT
   with prepended local namespace prefix becomes the value of its @name
   attribute.  If the 'leaf-list' statement has the 'min-elements'
   substatement and its argument is greater than one, additional
   attribute @nma:min-elements is attached to <rng:element> and the
   argument of 'min-elements' becomes the value of this attribute.
   Similarly, if there is the 'max-elements' substatement and its
   argument value is not "unbounded", attribute @nma:max-elements is
   attached to this element and the argument of 'max-elements' becomes
   the value of this attribute.

   EXAMPLE.  YANG leaf-list in a module with namespace prefix "yam"







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   leaf-list foliage {
       min-elements 3;
       max-elements 6378;
       ordered-by user;
       type string;
   }

   is mapped to the following RELAX NG fragment:

   <rng:oneOrMore>
     <rng:element name="yam:foliage" nma:ordered-by="user"
                  nma:min-elements="3" nma:max-elements="6378">
       <rng:data type="string"/>
     </rng:element>
   </rng:oneOrMore>

11.29.  The length Statement

   This statement is handled within the "string" type, see
   Section 11.53.9.

11.30.  The list Statement

   This statement is mapped exactly as the 'leaf-list' statement, see
   Section 11.28.

   When mapping the substatements of 'list', the order of children of
   the list element MUST be specified so that list keys, if there are
   any, always appear in the same order as they are defined in the input
   YANG module and before other children, see [YANG], Section 7.8.5.  In
   particular, if any list key is defined in a grouping but the list
   node itself is not a part of the same grouping, and the position of
   the 'uses' statement would violate the above ordering requirement,
   the grouping MUST be expanded, i.e., the 'uses' statement replaced by
   the grouping contents.

   For example, consider the following YANG fragment of a module with
   prefix "yam":













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   grouping keygrp {
       leaf clef {
           type uint8;
       }
   }

   list foo {
       key clef;
       leaf bar {
           type string;
       }
       leaf baz {
           type string;
       }
       uses keygrp;
   }

   is mapped to the following RELAX NG fragment:

   <rng:zeroOrMore>
     <rng:element name="yam:foo" nma:key="yam:clef">
       <rng:element name="yam:clef">
         <rng:data type="unsignedByte"/>
       </rng:element>
       <rng:interleave>
         <rng:element name="yam:bar">
           <rng:data type="string"/>
         </rng:element>
         <rng:element name="yam:baz">
           <rng:data type="string"/>
         </rng:element>
       </rng:interleave>
     </rng:element>
   </rng:zeroOrMore>

   Note that the "keygrp" grouping is expanded and the "yam:clef"
   definition moved before the <rng:interleave> pattern.

11.31.  The mandatory Statement

   This statement may appear as a substatement of 'leaf', 'choice' or
   'anyxml' statement.  If ARGUMENT is "true", the parent data node is
   mapped as mandatory, see Section 9.1.1.

11.32.  The max-elements Statement

   This statement is handled within 'leaf-list' or 'list' statements,
   see Section 11.28.



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11.33.  The min-elements Statement

   This statement is handled within 'leaf-list' or 'list' statements,
   see Section 11.28.

11.34.  The module Statement

   This statement is not specifically mapped except that a <dc:source>
   element SHOULD be created as a child of <rng:grammar> and contain
   ARGUMENT as a reference to the input YANG module.  See also
   Section 11.49.

   With respect to the conceptual tree schema, substatements of 'module'
   MUST be mapped so that

   o  top level data elements be defined as descendants of the <nmt:top>
      element;

   o  elements mapped from 'rpc' statements be defined as descendants of
      the <nmt:rpc-methods> element;

   o  elements mapped from 'notification' statements be defined as
      descendants of the <nmt:notifications> element.

11.35.  The must Statement

   This statement is mapped to the <nma:must> element.  It has one
   mandatory attribute @assert (with no namespace), which contains
   ARGUMENT transformed into a valid XPath expression (see Section 9.3).
   The <nma:must> element may get other subelements resulting from
   mapping 'error-app-tag' and 'error-message' substatements.  Other
   substatements of 'must', i.e., 'description' and 'reference', are
   ignored.

   EXAMPLE.  YANG statement

   must 'current() <= ../max-lease-time' {
       error-message
           "The default-lease-time must be less than max-lease-time";
   }

   is mapped to

   <nma:must assert="current()&lt;=../dhcp:max-lease-time">
     <nma:error-message>
       The default-lease-time must be less than max-lease-time
     </nma:error-message>
   </nma:must>



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11.36.  The namespace Statement

   This statement is mapped to @xmlns:xxx attribute of the <rng:grammar>
   element where "xxx" is the namespace prefix specified by the sibling
   'prefix' statement.  ARGUMENT becomes the value of this attribute.

11.37.  The notification Statement

   This statement is mapped to the following subtree in the RELAX NG
   schema ("yam" is the prefix of the local YANG module):

   <rng:element name="nmt:notification">
     <rng:element name="yam:ARGUMENT">
       ...
     </rng:element>
   </rng:element>

   Substatements of 'notification' are mapped under <rng:element
   name="yam:ARGUMENT">.

   The <rng:element name="nmt:rpc-notification"> element is a child of
   <rng:element name="nmt:notifications">.

11.38.  The ordered-by Statement

   This statement is mapped to @nma:ordered-by attribute and ARGUMENT
   becomes the value of this attribute.  See Section 11.28 for an
   example.

11.39.  The organization Statement

   This statement is not used by the mapping since the output conceptual
   tree schema may result from multiple YANG modules authored by
   different parties.  The schema contains references to all input
   modules in the Dublin Core elements <dc:source>, see Section 11.34.
   The original modules are the authoritative sources of the authorship
   information.

11.40.  The output Statement

   This statement is handled within 'rpc' statement, see Section 11.50.

11.41.  The path Statement

   This statement is handled within "leafref" type, see Section 11.53.7.






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11.42.  The pattern Statement

   This statement is handled within "string" type, see Section 11.53.9.

11.43.  The position Statement

   This statement is ignored.

11.44.  The prefix Statement

   This statement is handled within the sibling 'namespace' statement,
   see Section 11.36, or within the parent 'import' statement, see
   Section 11.23.  As a substatement of 'belongs-to' (in submodules),
   the 'prefix' statement is ignored.

11.45.  The presence Statement

   This statement is mapped to the annotation attribute @nma:presence
   with the value "true".  In addition, it influences the mapping of
   'container' (Section 11.11): the parent container definition MUST be
   wrapped in <rng:optional>, regardless of its content.  See also
   Section 9.1.1.

11.46.  The range Statement

   This statement is handled within numeric types, see Section 11.53.8.

11.47.  The reference Statement

   This statement MAY be ignored.  Otherwise, it is mapped to
   <a:documentation> element and its text is set to ARGUMENT prefixed
   with "See: ".

11.48.  The require-instance Statement

   This statement is handled within "instance-identifier" type
   (Section 11.53.6).

11.49.  The revision Statement

   The mapping uses only the most recent instance of the 'revision'
   statement, i.e., one with the latest date in ARGUMENT, which
   specifies the current revision of the input YANG module [YANG].  This
   date SHOULD be recorded, together with the name of the YANG module,
   in the corresponding Dublin Core element <dc:source> (see
   Section 11.34), for example in this form:

   <dc:source>YANG module 'foo', revision 2010-03-02</dc:source>



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   The 'description' substatement of 'revision' is ignored.

11.50.  The rpc Statement

   This statement is mapped to the following subtree in the RELAX NG
   schema ("yam" is the prefix of the local YANG module):

   <rng:element name="nmt:rpc-method">
     <rng:element name="nmt:input">
       <rng:element name="yam:ARGUMENT">
         ... mapped content of 'input' ...
       </rng:element>
     </rng:element>
     <rng:element name="nmt:output">
       ... mapped content of 'output' ...
     </rng:element>
   </rng:element>

   As indicated in the schema fragment, contents of the 'input'
   substatement (if any) are mapped under <rng:element name="yam:
   ARGUMENT">.  Similarly, contents of the 'output' substatement are
   mapped under <rng:element name="nmt:output">.  If there is no
   'output' substatement, the <rng:element name="nmt:output"> MUST NOT
   be present.

   The <rng:element name="nmt:rpc-method"> element is a child of <rng:
   element name="nmt:rpc-methods">.

11.51.  The status Statement

   This statement MAY be ignored.  Otherwise, it is mapped to @nma:
   status attribute and ARGUMENT becomes its value.

11.52.  The submodule Statement

   This statement is not specifically mapped.  Its substatements are
   mapped as if they appeared directly in the module the submodule
   belongs to.

11.53.  The type Statement

   Most YANG built-in datatypes have an equivalent in the XSD datatype
   library [XSD-D] as shown in Table 3.








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      +-----------+---------------+--------------------------------+
      | YANG type | XSD type      | Meaning                        |
      +-----------+---------------+--------------------------------+
      | int8      | byte          | 8-bit integer value            |
      |           |               |                                |
      | int16     | short         | 16-bit integer value           |
      |           |               |                                |
      | int32     | int           | 32-bit integer value           |
      |           |               |                                |
      | int64     | long          | 64-bit integer value           |
      |           |               |                                |
      | uint8     | unsignedByte  | 8-bit unsigned integer value   |
      |           |               |                                |
      | uint16    | unsignedShort | 16-bit unsigned integer value  |
      |           |               |                                |
      | uint32    | unsignedInt   | 32-bit unsigned integer value  |
      |           |               |                                |
      | uint64    | unsignedLong  | 64-bit unsigned integer value  |
      |           |               |                                |
      | string    | string        | character string               |
      |           |               |                                |
      | boolean   | boolean       | "true" or "false"              |
      |           |               |                                |
      | binary    | base64Binary  | binary data in base64 encoding |
      +-----------+---------------+--------------------------------+

     Table 3: YANG built-in datatypes with equivalents in the W3C XML
                            Schema Type Library

   Two important datatypes of the XSD datatype library - "dateTime" and
   "anyURI" - are not built-in in YANG but defined as derived types in
   the standard modules [Ytypes]: "date-and-time" in the "ietf-yang-
   types" module and "uri" in the "ietf-inet-types" module.  However,
   the formal restrictions in the YANG type definitions are rather weak.
   Therefore, implementations of the YANG-to-DSDL mapping SHOULD detect
   these derived types in source YANG modules and map them to "dateType"
   and "anyURI", respectively.

   Details about the mapping of individual YANG built-in types are given
   in the following subsections.

11.53.1.  The empty Type

   This type is mapped to <rng:empty/>.







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11.53.2.  The boolean and binary Types

   These two built-in types do not allow any restrictions and are mapped
   simply by inserting <rng:data> element whose @type attribute is set
   to ARGUMENT mapped according to Table 3 above.

11.53.3.  The bits Type

   This type is mapped to <rng:list> and for each 'bit' substatement the
   following XML fragment is inserted as a child of <rng:list>:

   <rng:optional>
     <rng:value>bit_name</rng:value>
   </rng:optional>

   where bit_name is the name of the bit as found in the argument of the
   corresponding 'bit' statement.

11.53.4.  The enumeration and union Types

   These types are mapped to <rng:choice> element.

11.53.5.  The identityref Type

   This type is mapped to <rng:choice> element with one or more <rng:
   value> subelements.  Each of the <rng:value> subelements MUST have
   the @type attribute and its value set to "QName".  One <rng:value>
   subelement for the base identity MUST always be present - it contains
   the argument of the 'base' substatement as its text.  In addition,
   one <rng:value> substatement MUST be added for each identity declared
   locally or in an imported module that is derived from this base
   identity.

   All namespace prefixes that are used for identities from imported
   modules MUST be appropriately defined.

   EXAMPLE (taken from Section 7.16.3 of [YANG]).  Consider the
   following two YANG modules:













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   module crypto-base {
       namespace "http://example.com/crypto-base";
       prefix "crypto";

       identity crypto-alg {
       description
           "Base identity from which all crypto algorithms
            are derived.";
       }
   }

   module des {
       namespace "http://example.com/des";
       prefix "des";

       import "crypto-base" {
           prefix "crypto";
       }

       identity des {
           base "crypto:crypto-alg";
           description "DES crypto algorithm";
       }

       identity des3 {
           base "crypto:crypto-alg";
           description "Triple DES crypto algorithm";
       }
   }

   If these two modules are imported to another module with namespace
   prefix "yam", leaf definition

   leaf crypto {
       type identityref {
           base "crypto:crypto-alg";
       }
   }

   is mapped to

   <rng:element name="yam:crypto">
     <rng:choice>
       <rng:value type="QName">crypto:crypto-alg</value>
       <rng:value type="QName">des:des</value>
       <rng:value type="QName">des:des3</value>
    </rng:choice>
   </rng:element>



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   The "crypto" and "des" prefixes will typically be defined via
   attributes of the <rng:grammar> element.

11.53.6.  The instance-identifier Type

   This type is mapped to <rng:data> element with @type attribute set to
   "string".  In addition, empty <nma:instance-identifier> element MUST
   be inserted as a child of PARENT.

   The argument of the 'require-instance' substatement, if it exists,
   becomes the value of the @require-instance attribute of <nma:
   instance-identifier>.

11.53.7.  The leafref Type

   This type is mapped exactly as the type of the leaf given in the
   argument of 'path' substatement.  In addition, @nma:leafref attribute
   MUST be added to PARENT.  The argument of the 'path' substatement,
   translated according to Section 9.3, is set as the value of this
   attribute.

11.53.8.  The numeric Types

   YANG built-in numeric types are "int8", "int16", "int32", "int64",
   "uint8", "uint16", "uint32", "uint64" and "decimal64".  They are
   mapped to <rng:data> element with @type attribute set to ARGUMENT
   translated according to Table 3 above.

   An exception is the "decimal64" type, which is mapped to the
   "decimal" type of the XSD datatype library.  Its precision and number
   of fractional digits are controlled with the following facets, which
   MUST always be present:

   o  "totalDigits" facet set to the value of 19.

   o  "fractionDigits" facet set to the argument of the 'fraction-
      digits' substatement.

   The fixed value of "totalDigits" corresponds to the maximum of 19
   decimal digits for 64-bit integers.

   For example, the statement

   type decimal64 {
       fraction-digits 2;
   }

   is mapped to the following RELAX NG datatype:



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   <rng:data type="decimal">
     <rng:param name="totalDigits">19</rng:param>
     <rng:param name="fractionDigits">2</rng:param>
   </rng:data>

   All numeric types support the 'range' restriction, which is handled
   as follows:

   If the range expression has just a single range, then

   o  if the range consists of a single number, the <rng:value> pattern
      is inserted and its content set to this number.

   o  Otherwise the range consists of both lower and upper bound and the
      following pair of datatype facets are inserted:

         <rng:param name="minInclusive">...</rng:param>

      and

          <rng:param name="maxInclusive">...</rng:param>

      Their contents are the lower and upper bound, respectively.  If
      the lower bound is "min", the "minInclusive" facet is omitted and
      if the upper bound is "max", the "maxInclusive" facet is omitted.

   If the range expression has multiple parts separated by "|", then the
   parent <rng:data> element must be repeated once for every range part
   and all such <rng:data> elements are wrapped in <rng:choice> element.
   Each <rng:data> element contains the <rng:value> pattern or the
   "minInclusive" and "maxInclusive" facets for one part of the range
   expression as described in the previous paragraph.  For the
   "decimal64" type, the "totalDigits" and "fractionDigits" must be
   repeated inside each of the <rng:data> elements.

   For example,

   type int32 {
       range "-6378..0|42|100..max";
   }

   is mapped to the following RELAX NG fragment:









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   <rng:choice>
     <rng:data type="int">
       <rng:param name="minInclusive">-6378</rng:param>
       <rng:param name="maxInclusive">0</rng:param>
     </rng:data>
     <rng:data type="int">
       <rng:value>42</rng:value>
     </rng:data>
     <rng:data type="int">
       <rng:param name="minInclusive">100</rng:param>
     </rng:data>
   </rng:choice>

11.53.9.  The string Type

   This type is mapped to <rng:data> element with the @type attribute
   set to "string".

   The 'length' restriction is handled analogically to the 'range'
   restriction for the numeric types (Section 11.53.8):

   If the length expression has just a single range, then

   o  if the length range consists of a single number L, the following
      datatype facet is inserted:

         <rng:param name="length">L</rng:param>.

   o  Otherwise the length range consists of both lower and upper bound
      and the following pair of datatype facets are inserted:

         <rng:param name="minLength">...</rng:param>

      and

         <rng:param name="maxLength">...</rng:param>

      Their contents are the lower and upper bound of the length range,
      respectively.  If the lower bound is "min", the "minLength" facet
      is omitted and if the upper bound is "max", the "maxLength" facet
      is omitted.

   If the length expression has of multiple parts separated by "|", then
   the parent <rng:data> element must be repeated once for every range
   part and all such <rng:data> elements are wrapped in <rng:choice>
   element.  Each <rng:data> element contains the "length" or
   "minLength" and "maxLength" facets for one part of the length
   expression as described in the previous paragraph.



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   Every 'pattern' restriction of the "string" datatype is mapped to the
   "pattern" facet

   <rng:param name="pattern">...</rng:param>

   with content equal to the argument of the 'pattern' statement.  All
   such "pattern" facets must be repeated inside each copy of the <rng:
   data> element, i.e., once for each length range.

   For example,

   type string {
       length "1|3..8";
       pattern "[A-Z][a-z]*";
   }

   is mapped to the following RELAX NG fragment:

   <rng:choice>
     <rng:data type="string">
       <rng:param name="length">1</rng:param>
       <rng:param name="pattern">[A-Z][a-z]*</rng:param>
     </rng:data>
     <rng:data type="string">
       <rng:param name="minLength">3</rng:param>
       <rng:param name="maxLength">8</rng:param>
       <rng:param name="pattern">[A-Z][a-z]*</rng:param>
     </rng:data>
   </rng:choice>

11.53.10.  Derived Types

   If the 'type' statement refers to a derived type, it is mapped in one
   of the following ways depending on whether it contains any
   restrictions as its substatements:

   1.  Without restrictions, the 'type' statement is mapped simply to
       the <rng:ref> element, i.e., a reference to a named pattern.  If
       the RELAX NG definition of this named pattern has not been added
       to the output schema yet, the corresponding type definition MUST
       be found and its mapping installed as a subelement of <rng:
       grammar>, see Section 11.54.  Even if a given derived type is
       used more than once in the input YANG modules, the mapping of the
       corresponding 'typedef' MUST be installed only once.

   2.  If any restrictions are present, the ancestor built-in type for
       the given derived type must be determined and the mapping of this
       base type MUST be used.  Restrictions appearing at all stages of



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       the type derivation chain MUST be taken into account and their
       conjunction added to the <rng:data> element which defines the
       basic type.

   See Section 9.2.2 for more details and an example.

11.54.  The typedef Statement

   This statement is mapped to a RELAX NG named pattern definition <rng:
   define>, but only if the type defined by this statement is used
   without restrictions in at least one of the input modules.  In this
   case, the named pattern definition becomes a child of the <rng:
   grammar> element and its name is ARGUMENT mangled according to the
   rules specified in Section 9.2.

   Whenever a derived type is used with additional restrictions, the
   ancestor built-in type for the derived type is used instead with
   restrictions (facets) that are a combination of all restrictions
   specified along the type derivation chain.  See Section 11.53.10 for
   further details and an example.

   An implementation MAY offer the option of recording all 'typedef'
   statements as named patterns in the output RELAX NG schema even if
   they are not referenced.  This is useful for mapping YANG "library"
   modules containing only 'typedef' and/or 'grouping' statements.

11.55.  The unique Statement

   This statement is mapped to @nma:unique attribute.  ARGUMENT is
   translated so that every node identifier in each of its components is
   prefixed with the namespace prefix of the local module, unless the
   prefix is already present.  The result of this translation then
   becomes the value of the @nma:unique attribute.

   For example, assuming that the local module prefix is "ex",

   unique "foo ex:bar/baz"

   is mapped to the following attribute/value pair:

   nma:unique="ex:foo ex:bar/ex:baz"

11.56.  The units Statement

   This statement is mapped to @nma:units attribute and ARGUMENT becomes
   its value.  Implementations MAY ignore this statement.





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11.57.  The uses Statement

   If this statement has neither 'refine' nor 'augment' substatements,
   it is mapped to <rng:ref> element, i.e., a reference to a named
   pattern, and the value of its @name attribute is set to ARGUMENT
   mangled according to Section 9.2.  If the RELAX NG definition of the
   referenced named pattern has not been added to the output schema yet,
   the corresponding grouping MUST be found and its mapping installed as
   a subelement of <rng:grammar>, see Section 11.20.

   Otherwise, if the 'uses' statement has any 'refine' or 'augment'
   substatements, the corresponding grouping must be looked up and its
   contents is inserted under PARENT.  See Section 9.2.1 for further
   details and an example.

11.58.  The value Statement

   This statement is ignored.

11.59.  The when Statement

   This statement is mapped to @nma:when attribute and ARGUMENT,
   translated according to Section 9.3, becomes it value.

11.60.  The yang-version Statement

   This statement is not mapped to the output schema.  However, an
   implementation SHOULD check that it is compatible with the YANG
   version declared by the statement (currently version 1).

11.61.  The yin-element Statement

   This statement is not mapped to the output schema, but see the rules
   for extension handling in Section 9.4.

















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12.  Mapping NETMOD-specific annotations to DSDL Schema Languages

   This section contains mapping specification for individual NETMOD-
   specific annotations.  In each case, the result of the mapping must
   be inserted into an appropriate context of the target DSDL schema as
   described in Section 10.  The context is determined by the element
   definition in the conceptual tree schema to which the annotation is
   attached.  In the rest of this section, we will denote CONTELEM the
   name of this context element properly qualified with its namespace
   prefix.  Unless otherwise stated, Schematron asserts are descendants
   of the "standard" pattern and therefore active in both validation
   phases.

12.1.  The @nma:config Annotation

   If this annotation is present with the value "false", the following
   rules MUST be observed for DSDL schemas of <nc:get-config> reply:

   o  When generating RELAX NG, the contents of the CONTELEM definition
      MUST be changed to <rng:notAllowed>.

   o  When generating Schematron or DSRL, the CONTELEM definition and
      all its descendants in the conceptual tree schema MUST be ignored.

12.2.  The @nma:default Annotation

   This annotation is used for generating the DSRL schema as described
   in Section 10.4.

12.3.  The @nma:implicit Annotation

   This annotation is used for generating the DSRL schema as described
   in Section 10.4.

12.4.  The <nma:error-app-tag> Annotation

   This annotation currently has no mapping defined.

12.5.  The <nma:error-message> Annotation

   This annotation is handled within <nma:must>, see Section 12.11.

12.6.  The <nma:instance-identifier> Annotation

   If this annotation element has the @require-instance attribute with
   the value "false", it is ignored.  Otherwise it is mapped to the
   following Schematron assert:




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   <sch:assert test="nmf:evaluate(.)">
     The element pointed to by "CONTELEM" must exist.
   </sch:assert>

   The nmf:evaluate() function is an XSLT extension function (see
   Extension Functions in [XSLT]) that evaluates an XPath expression at
   runtime.  Such an extension function is provided by some XSLT
   processors, for example Saxon [3].

12.7.  The @nma:key Annotation

   Assume this annotation attribute has the value "k_1 k_2 ... k_n",
   i.e., specifies n children of CONTELEM as list keys.  The annotation
   is then mapped to the following Schematron report:

   <sch:report test="CONDITION">
     Duplicate key of list "CONTELEM"
   </sch:report>

   where CONDITION has this form:
   preceding-sibling::CONTELEM[C_1 and C_2 and ... and C_n]

   Each sub-expression C_i, for i=1,2,...,n, specifies the condition for
   violation of uniqueness of key k_i, namely

   k_i=current()/k_i

12.8.  The @nma:leafref Annotation

   This annotation is mapped to the following assert:

   <sch:assert test="PATH=.">
     Leafref "CONTELEM" must have the same value as "PATH"
   </sch:assert>

   where PATH is the value of @nma:leafref.  The assert is a descendant
   of the "ref-integrity" pattern, which means that it will be used only
   for the "full" validation phase.

12.9.  The @nma:min-elements Annotation

   This annotation is mapped to the following Schematron assert:

   <sch:assert test="count(../CONTELEM)&gt;=MIN">
     List "CONTELEM" - item count must be at least MIN
   </sch:assert>

   where MIN is the value of @nma:min-elements.



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12.10.  The @nma:max-elements Annotation

   This annotation is mapped to the following Schematron assert:

   <sch:assert test="count(../CONTELEM)&lt;=MAX">
     List "CONTELEM" - item count must be at most MAX
   </sch:assert>

   where MAX is the value of @nma:min-elements.

12.11.  The <nma:must> Annotation

   This annotation is mapped to the following Schematron assert:

   <sch:assert test="EXPRESSION">
     MESSAGE
   </sch:assert>

   where EXPRESSION is the value of the mandatory @assert attribute of
   <nma:must>.  If the <nma:error-message> subelement exists, MESSAGE is
   set to its content, otherwise it is set to the default message
   "Condition EXPRESSION must be true".

12.12.  The <nma:ordered-by> Annotation

   This annotation currently has no mapping defined.

12.13.  The <nma:status> Annotation

   This annotation currently has no mapping defined.

12.14.  The @nma:unique Annotation

   The mapping of this annotation is almost identical as for @nma:key,
   see Section 12.7, with two small differences:

   o  The value of @nma:unique is a list of descendant schema node
      identifiers rather than simple leaf names.  However, the XPath
      expressions specified in Section 12.7 work without any
      modifications if the descendant schema node identifiers are
      substituted for k_1, k_2, ..., k_n.

   o  The message appearing as the text of <sch:report> is different:
      "Violated uniqueness for list CONTELEM".







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12.15.  The @nma:when Annotation

   This annotation is mapped to the following Schematron assert:

   <sch:assert test="EXPRESSION">
     Node "CONTELEM" is only valid when "EXPRESSION" is true.
   </sch:assert>

   where EXPRESSION is the value of @nma:when.










































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13.  IANA Considerations

   This document registers three namespace URIs in the IETF XML registry
   [RFC3688]:
   URI: urn:ietf:params:xml:ns:netmod:dsdl-annotations:1
   URI: urn:ietf:params:xml:ns:netmod:conceptual-tree:1
   URI: urn:ietf:params:xml:ns:netmod:xpath-extensions:1












































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14.  Security Considerations

   This document defines a procedure that maps data models expressed in
   the YANG language to a coordinated set of DSDL schemas.  The
   procedure itself has no security impact on the Internet.

   DSDL schemas obtained by the mapping procedure may be used for
   validating the content of NETCONF protocol data units or entire
   datastores and thus provide additional validity checks above those
   performed by NETCONF server and client implementations supporting
   YANG data models.  The strictness of this validation is directly
   derived from the source YANG modules that the validated XML data
   adhere to.






































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15.  Acknowledgments

   The authors wish to thank the following individuals who provided
   helpful suggestions and/or comments on various versions of this
   document: Andy Bierman, Martin Bjorklund, Jirka Kosek and Phil
   Shafer.













































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16.  References

16.1.  Normative References

   [DSDL]     ISO/IEC, "Document Schema Definition Languages (DSDL) -
              Part 1: Overview", ISO/IEC 19757-1, 11 2004.

   [DSRL]     ISO/IEC, "Information Technology - Document Schema
              Definition Languages (DSDL) - Part 8: Document Semantics
              Renaming Language - DSRL", ISO/IEC 19757-8:2008(E),
              12 2008.

   [NVDL]     ISO/IEC, "Information Technology - Document Schema
              Definition Languages (DSDL) - Part 4: Namespace-Based
              Validation Dispatching Language (NVDL)", ISO/
              IEC 19757-4:2006(E), 6 2006.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              January 2004.

   [RFC4741]  Enns, R., "NETCONF Configuration Protocol", RFC 4741,
              December 2006.

   [RFC5013]  Kunze, J., "The Dublin Core Metadata Element Set",
              RFC 5013, August 2007.

   [RNG]      ISO/IEC, "Information Technology - Document Schema
              Definition Languages (DSDL) - Part 2: Regular-Grammar-
              Based Validation - RELAX NG. Second Edition.", ISO/
              IEC 19757-2:2008(E), 12 2008.

   [RNG-CS]   ISO/IEC, "Information Technology - Document Schema
              Definition Languages (DSDL) - Part 2: Regular-Grammar-
              Based Validation - RELAX NG. AMENDMENT 1: Compact Syntax",
              ISO/IEC 19757-2:2003/Amd. 1:2006(E), 1 2006.

   [RNG-DTD]  Clark, J., Ed. and M. Murata, Ed., "RELAX NG DTD
              Compatibility", OASIS Committee Specification 3 December
              2001, December 2001.

   [Schematron]
              ISO/IEC, "Information Technology - Document Schema
              Definition Languages (DSDL) - Part 3: Rule-Based
              Validation - Schematron", ISO/IEC 19757-3:2006(E), 6 2006.




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   [XML]      Bray, T., Paoli, J., Sperberg-McQueen, C., Maler, E., and
              F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fifth
              Edition)", World Wide Web Consortium Recommendation REC-
              xml-20081126, November 2008,
              <http://www.w3.org/TR/2006/REC-xml-20060816>.

   [XPath]    Clark, J. and S. DeRose, "XML Path Language (XPath)
              Version 1.0", World Wide Web Consortium
              Recommendation REC-xpath-19991116, November 1999,
              <http://www.w3.org/TR/1999/REC-xpath-19991116>.

   [XSD-D]    Biron, P. and A. Malhotra, "XML Schema Part 2: Datatypes
              Second Edition", World Wide Web Consortium
              Recommendation REC-xmlschema-2-20041028, October 2004,
              <http://www.w3.org/TR/2004/REC-xmlschema-2-20041028>.

   [XSLT]     Clark, J., "XSL Transformations (XSLT) Version 1.0", World
              Wide Web Consortium Recommendation REC-xslt-19991116,
              November 1999.

   [YANG]     Bjorklund, M., Ed., "YANG - A data modeling language for
              NETCONF", draft-ietf-netmod-yang-11 (work in progress),
              Febuary 2010.

   [Ytypes]   Schoenwaelder, J., Ed., "Common YANG Data Types",
              draft-ietf-netmod-yang-types-07 (work in progress),
              February 2010.

16.2.  Informative References

   [RFC1157]  Case, J., Fedor, M., Schoffstall, M., and J. Davin,
              "Simple Network Management Protocol (SNMP)", STD 15,
              RFC 1157, May 1990.

   [RFC2578]  McCloghrie, K., Ed., Perkins, D., Ed., and J.
              Schoenwaelder, Ed., "Structure of Management Information
              Version 2 (SMIv2)", STD 58, RFC 2578, April 1999.

   [RFC3216]  Elliott, C., Harrington, D., Jason, J., Schoenwaelder, J.,
              Strauss, F., and W. Weiss, "SMIng Objectives", RFC 3216,
              December 2001.

   [RFC5277]  Chisholm, S. and H. Trevino, "NETCONF Event
              Notifications", RFC 5277, July 2008.

   [Vli04]    van der Vlist, E., "RELAX NG", O'Reilly , 2004.

   [XSD]      Thompson, H., Beech, D., Maloney, M., and N. Mendelsohn,



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              "XML Schema Part 1: Structures Second Edition", World Wide
              Web Consortium Recommendation REC-xmlschema-1-20041028,
              October 2004,
              <http://www.w3.org/TR/2004/REC-xmlschema-1-20041028>.















































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URIs

   [1]  <http://www.thaiopensource.com/relaxng/trang.html>

   [2]  <http://dublincore.org/>

   [3]  <http://www.saxonica.com/>

   [4]  <http://www.yang-central.org/twiki/bin/view/Main/DhcpTutorial>

   [5]  <http://code.google.com/p/pyang/>

   [6]  <http://thaiopensource.com/relaxng/trang.html>






































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Appendix A.  Schemas for NETMOD-Specific Annotations

   This appendix utilizes Namespace-Based Validation Dispatching
   Language (NVDL, Part 4 of DSDL) [NVDL] to define NETMOD-specific
   annotations as extensions of the RELAX NG language.  The NVDL schema
   may be used for validating conceptual tree schemas as compound XML
   documents consisting of RELAX NG sections and embedded sections with
   NETMOD-specific annotations.  The NVDL schema dispatches the
   validation as follows:

   1.  RELAX NG sections identified by the namespace URI
       "http://relaxng.org/ns/structure/1.0" is validated with the
       standard RELAX NG schema for RELAX NG, see [RNG], Annex A.

   2.  NETMOD-specific annotation sections identified by the namespace
       URI "urn:ietf:params:xml:ns:netmod:dsdl-annotations:1" are
       validated by several context-dependent RELAX NG schemas given
       below.

   3.  Other sections such as Dublin Core metadata or <a:documentation>
       annotation are attached to and validated together with the parent
       RELAX NG section.

A.1.  NVDL Schema

   <CODE BEGINS> file "nmannot.nvdl"

   <?xml version="1.0" encoding="UTF-8"?>
   <!DOCTYPE nvdl:rules [<!ENTITY nmannot-uri
     "urn:ietf:params:xml:ns:netmod:dsdl-annotations:1">
   ]>
   <rules xmlns="http://purl.oclc.org/dsdl/nvdl/ns/structure/1.0"
          startMode="rng">
     <mode name="rng">
       <namespace ns="http://relaxng.org/ns/structure/1.0">
         <validate schema="http://relaxng.org/relaxng.rng"
                   useMode="other">
           <context path="define" useMode="define"/>
           <context path="oneOrMore/element" useMode="list"/>
           <context path="element" useMode="element"/>
           <context path="choice/group|choice/interleave"
                    useMode="group-interleave"/>
           <context path="choice|ref" useMode="choice-ref"/>
           <context path="value" useMode="value"/>
         </validate>
       </namespace>
     </mode>
     <mode name="define">



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       <namespace ns="&nmannot-uri;" match="attributes">
         <validate schema="define.rng"/>
       </namespace>
     </mode>
     <mode name="element">
       <namespace ns="&nmannot-uri;" match="elements">
         <validate schema="element-el.rng"/>
       </namespace>
       <namespace ns="&nmannot-uri;" match="attributes">
         <validate schema="element-att.rng"/>
       </namespace>
     </mode>
     <mode name="group-interleave">
       <namespace ns="&nmannot-uri;" match="attributes">
         <validate schema="group-interleave.rng"/>
       </namespace>
     </mode>
     <mode name="choice-ref">
       <namespace ns="&nmannot-uri;" match="attributes">
         <validate schema="choice-ref.rng"/>
       </namespace>
     </mode>
     <mode name="list">
       <namespace ns="&nmannot-uri;" match="attributes">
         <validate schema="list.rng"/>
       </namespace>
     </mode>
     <mode name="value">
       <namespace ns="&nmannot-uri;" match="attributes">
         <validate schema="value.rng"/>
       </namespace>
     </mode>
     <mode name="other">
       <namespace ns="&nmannot-uri;" match="elements attributes">
         <reject/>
       </namespace>
       <anyNamespace match="elements attributes">
         <attach/>
       </anyNamespace>
     </mode>
   </rules>

   <CODE ENDS>








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A.2.  Annotation Attributes for define Pattern

   <CODE BEGINS> file "define.rng"

   <?xml version="1.0" encoding="UTF-8"?>
   <grammar xmlns="http://relaxng.org/ns/structure/1.0">
     <include href="nmannotdefs.rng"/>
     <start>
       <group>
         <ref name="default-attribute"/>
         <ref name="status-attribute"/>
         <ref name="units-attribute"/>
       </group>
     </start>
   </grammar>

   <CODE ENDS>

A.3.  Annotation Elements for element Pattern

   <CODE BEGINS> file "element-el.rng"

   <?xml version="1.0" encoding="UTF-8"?>
   <grammar xmlns="http://relaxng.org/ns/structure/1.0">
     <include href="nmannotdefs.rng"/>
     <start>
       <choice>
         <ref name="must-element"/>
         <ref name="instance-identifier-element"/>
       </choice>
     </start>
   </grammar>

   <CODE ENDS>

















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A.4.  Annotation Attributes for element Pattern

   <CODE BEGINS> file "element-att.rng"

   <?xml version="1.0" encoding="UTF-8"?>
   <grammar xmlns="http://relaxng.org/ns/structure/1.0">
     <include href="nmannotdefs.rng"/>
     <start>
       <group>
         <ref name="config-attribute"/>
         <ref name="default-attribute"/>
         <ref name="implicit-attribute"/>
         <ref name="leafref-attribute"/>
         <ref name="presence-attribute"/>
         <ref name="status-attribute"/>
         <ref name="units-attribute"/>
         <ref name="when-attribute"/>
       </group>
     </start>
   </grammar>

   <CODE ENDS>

A.5.  Annotation attributes for group Pattern

   <CODE BEGINS> file "group-interleave.rng"

   <?xml version="1.0" encoding="UTF-8"?>
   <grammar xmlns="http://relaxng.org/ns/structure/1.0">
     <include href="nmannotdefs.rng"/>
     <start>
       <group>
         <ref name="implicit-attribute"/>
         <ref name="status-attribute"/>
         <ref name="when-attribute"/>
       </group>
     </start>
   </grammar>

   <CODE ENDS>











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A.6.  Annotation attributes for choice and ref Patterns

   <CODE BEGINS> file "choice-ref.rng"

   <?xml version="1.0" encoding="UTF-8"?>
   <grammar xmlns="http://relaxng.org/ns/structure/1.0">
     <include href="nmannotdefs.rng"/>
     <start>
       <group>
         <ref name="status-attribute"/>
         <ref name="when-attribute"/>
       </group>
     </start>
   </grammar>

   <CODE ENDS>

A.7.  Annotation attributes for element Pattern in the List Context

   <CODE BEGINS> file "list.rng"

   <?xml version="1.0" encoding="UTF-8"?>
   <grammar xmlns="http://relaxng.org/ns/structure/1.0">
     <include href="nmannotdefs.rng"/>
     <start>
       <group>
         <ref name="key-attribute"/>
         <ref name="min-elements-attribute"/>
         <ref name="max-elements-attribute"/>
         <ref name="ordered-by-attribute"/>
         <ref name="unique-attribute"/>
       </group>
     </start>
   </grammar>

   <CODE ENDS>















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A.8.  Annotation attributes for value Pattern

   <CODE BEGINS> file "value.rng"

   <?xml version="1.0" encoding="UTF-8"?>
   <grammar xmlns="http://relaxng.org/ns/structure/1.0">
     <include href="nmannotdefs.rng"/>
     <start>
       <ref name="status-attribute"/>
     </start>
   </grammar>

   <CODE ENDS>

A.9.  Named Patterns for All NETMOD-Specific Annotations

  <CODE BEGINS> file "nmannotdefs.rng"

  <?xml version="1.0" encoding="UTF-8"?>
  <grammar xmlns="http://relaxng.org/ns/structure/1.0"
           xmlns:nma="urn:ietf:params:xml:ns:netmod:dsdl-annotations:1"
           datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes">

  <define name="config-attribute">
    <optional>
      <attribute name="nma:config">
        <data type="boolean"/>
      </attribute>
    </optional>
  </define>

  <define name="default-attribute">
    <optional>
      <attribute name="nma:default"/>
    </optional>
  </define>

  <define name="implicit-attribute">
    <optional>
      <attribute name="nma:implicit">
        <data type="boolean"/>
      </attribute>
    </optional>
  </define>

  <define name="error-app-tag-element">
    <optional>
      <element name="nma:error-app-tag">



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        <text/>
      </element>
    </optional>
  </define>

  <define name="error-message-element">
    <optional>
      <element name="nma:error-message">
        <text/>
      </element>
    </optional>
  </define>

  <define name="instance-identifier-element">
    <element name="nma:instance-identifier">
      <optional>
        <attribute name="nma:require-instance">
          <data type="boolean"/>
        </attribute>
      </optional>
    </element>
  </define>

  <define name="key-attribute">
    <optional>
      <attribute name="nma:key">
        <list>
          <data type="QName"/>
        </list>
      </attribute>
    </optional>
  </define>

  <define name="leafref-attribute">
    <optional>
      <attribute name="nma:leafref">
        <data type="string"/>
      </attribute>
    </optional>
  </define>

  <define name="min-elements-attribute">
    <optional>
      <attribute name="nma:min-elements">
        <data type="nonNegativeInteger"/>
      </attribute>
    </optional>
  </define>



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  <define name="max-elements-attribute">
    <optional>
      <attribute name="nma:max-elements">
        <data type="nonNegativeInteger"/>
      </attribute>
    </optional>
  </define>

  <define name="must-element">
      <element name="nma:must">
        <attribute name="assert">
          <data type="string"/>
        </attribute>
        <interleave>
          <ref name="error-app-tag-element"/>
          <ref name="error-message-element"/>
        </interleave>
      </element>
  </define>

  <define name="ordered-by-attribute">
    <optional>
      <attribute name="nma:ordered-by">
        <choice>
          <value>user</value>
          <value>system</value>
        </choice>
      </attribute>
    </optional>
  </define>

  <define name="presence-attribute">
    <optional>
      <attribute name="nma:presence">
        <value>true</value>
      </attribute>
    </optional>
  </define>

  <define name="status-attribute">
    <optional>
      <attribute name="nma:status">
        <choice>
          <value>current</value>
          <value>deprecated</value>
          <value>obsolete</value>
        </choice>
      </attribute>



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    </optional>
  </define>

  <define name="unique-attribute">
    <optional>
      <attribute name="nma:unique">
        <list>
          <data type="token"/>
        </list>
      </attribute>
    </optional>
  </define>

  <define name="units-attribute">
    <optional>
      <attribute name="nma:units">
        <data type="string"/>
      </attribute>
    </optional>
  </define>

  <define name="when-attribute">
    <optional>
      <attribute name="nma:when">
        <data type="string"/>
      </attribute>
    </optional>
  </define>

  </grammar>

  <CODE ENDS>



















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Appendix B.  Schema-Independent Library

   In order to avoid copying the common named pattern definitions to
   every RELAX NG schema generated in the second mapping step, the
   definitions are collected in a library file - schema-independent
   library - which is included by the validating schemas under the file
   name "relaxng-lib.rng" (XML syntax) and "relaxng-lib.rnc" (compact
   syntax).  The included definitions cover patterns for common elements
   from base NETCONF [RFC4741] and event notifications [RFC5277].

  <CODE BEGINS> file "relaxng-lib.rng"

  <?xml version="1.0" encoding="UTF-8"?>

  <grammar xmlns="http://relaxng.org/ns/structure/1.0"
           xmlns:nc="urn:ietf:params:xml:ns:netconf:base:1.0"
           xmlns:en="urn:ietf:params:xml:ns:netconf:notification:1.0"
           datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes">

    <define name="message-id-attribute">
      <attribute name="message-id">
        <data type="string">
          <param name="maxLength">4095</param>
        </data>
      </attribute>
    </define>

    <define name="ok-element">
      <element name="nc:ok">
        <empty/>
      </element>
    </define>

    <define name="eventTime-element">
      <element name="en:eventTime">
        <data type="dateTime"/>
      </element>
    </define>
  </grammar>

  <CODE ENDS>










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Appendix C.  Mapping DHCP Data Model - A Complete Example

   This appendix demonstrates both steps of the YANG-to-DSDL mapping
   applied to the "canonical" DHCP tutorial [4] data model.  The single
   input YANG module is shown in Appendix C.1 and the output schemas in
   the following two subsections.

   The conceptual tree schema was obtained by the "rng" plugin of the
   pyang [5] tool and the validating DSDL schemas by XSLT stylesheets
   that are also part of pyang distribution.  RELAX NG schemas are shown
   in both XML and compact syntax.  The latter was obtained from the
   former by using the Trang tool [6]

   Due to the limit of 72 characters per line, few long strings required
   manual editing, in particular the regular expression patterns for IP
   addresses etc. in the RELAX NG schemas.  In the compact syntax we
   broke the patterns to appropriate segments and joined them with the
   concatenation operator "~".  In the XML syntax, though, the long
   patterns had to be replaced by the placeholder string "... regex
   pattern ...".  Also, line breaks were added to several documentation
   strings and Schematron messages.  Other than that, the results of the
   automatic translations were not changed.

C.1.  Input YANG Module

   module dhcp {
     namespace "http://example.com/ns/dhcp";
     prefix dhcp;

     import ietf-yang-types { prefix yang; }
     import ietf-inet-types { prefix inet; }

     organization
       "yang-central.org";
     description
       "Partial data model for DHCP, based on the config of
        the ISC DHCP reference implementation.";

     container dhcp {
       description
         "configuration and operational parameters for a DHCP server.";

       leaf max-lease-time {
         type uint32;
         units seconds;
         default 7200;
       }




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       leaf default-lease-time {
         type uint32;
         units seconds;
         must '. <= ../max-lease-time' {
           error-message
             "The default-lease-time must be less than max-lease-time";
         }
         default 600;
       }

       uses subnet-list;

       container shared-networks {
         list shared-network {
           key name;

           leaf name {
             type string;
           }
           uses subnet-list;
         }
       }

       container status {
         config false;
         list leases {
           key address;

           leaf address {
             type inet:ip-address;
           }
           leaf starts {
             type yang:date-and-time;
           }
           leaf ends {
             type yang:date-and-time;
           }
           container hardware {
             leaf type {
               type enumeration {
                 enum "ethernet";
                 enum "token-ring";
                 enum "fddi";
               }
             }
             leaf address {
               type yang:phys-address;
             }



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           }
         }
       }
     }

     grouping subnet-list {
       description "A reusable list of subnets";
       list subnet {
         key net;
         leaf net {
           type inet:ip-prefix;
         }
         container range {
           presence "enables dynamic address assignment";
           leaf dynamic-bootp {
             type empty;
             description
               "Allows BOOTP clients to get addresses in this range";
           }
           leaf low {
             type inet:ip-address;
             mandatory true;
           }
           leaf high {
             type inet:ip-address;
             mandatory true;
           }
         }

         container dhcp-options {
           description "Options in the DHCP protocol";
           leaf-list router {
             type inet:host;
             ordered-by user;
             reference "RFC 2132, sec. 3.8";
           }
           leaf domain-name {
             type inet:domain-name;
             reference "RFC 2132, sec. 3.17";
           }
         }

         leaf max-lease-time {
           type uint32;
           units seconds;
           default 7200;
         }
       }



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     }
   }

C.2.  Conceptual Tree Schema

C.2.1.  XML Syntax

   <?xml version="1.0" encoding="UTF-8"?>
   <grammar
       xmlns="http://relaxng.org/ns/structure/1.0"
       xmlns:a="http://relaxng.org/ns/compatibility/annotations/1.0"
       xmlns:dc="http://purl.org/dc/terms"
       xmlns:dhcp="http://example.com/ns/dhcp"
       xmlns:nma="urn:ietf:params:xml:ns:netmod:dsdl-annotations:1"
       xmlns:nmt="urn:ietf:params:xml:ns:netmod:conceptual-tree:1"
       datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes">
    <dc:creator>Pyang 0.9.3, CTS plugin</dc:creator>
    <dc:source>YANG module 'dhcp'</dc:source>
    <start>
     <element name="nmt:netmod-tree">
      <element name="nmt:top">
       <interleave>
        <optional>
         <element name="dhcp:dhcp" nma:implicit="true">
          <interleave>
           <a:documentation>
            configuration and operational parameters for a DHCP server
           </a:documentation>
           <optional>
            <element name="dhcp:max-lease-time"
                     nma:default="7200" nma:units="seconds">
             <data type="unsignedInt"/>
            </element>
           </optional>
           <optional>
            <element name="dhcp:default-lease-time"
                     nma:default="600" nma:units="seconds">
             <data type="unsignedInt"/>
             <nma:must assert=". &lt;= ../dhcp:max-lease-time">
              <nma:error-message>
               The default-lease-time must be less than max-lease-time.
              </nma:error-message>
             </nma:must>
            </element>
           </optional>
           <ref name="_dhcp__subnet-list"/>
           <optional>
            <element name="dhcp:shared-networks">



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             <interleave>
              <zeroOrMore>
               <element name="dhcp:shared-network"
                        nma:key="dhcp:name">
                <element name="dhcp:name">
                 <data type="string"/>
                </element>
                <interleave>
                 <ref name="_dhcp__subnet-list"/>
                </interleave>
               </element>
              </zeroOrMore>
             </interleave>
            </element>
           </optional>
           <optional>
            <element name="dhcp:status" nma:config="false">
             <interleave>
              <zeroOrMore>
               <element name="dhcp:leases"
                        nma:key="dhcp:address">
                <element name="dhcp:address">
                 <ref name="ietf-inet-types__ip-address"/>
                </element>
                <interleave>
                 <optional>
                  <element name="dhcp:starts">
                   <ref name="ietf-yang-types__date-and-time"/>
                  </element>
                 </optional>
                 <optional>
                  <element name="dhcp:ends">
                   <ref name="ietf-yang-types__date-and-time"/>
                  </element>
                 </optional>
                 <optional>
                  <element name="dhcp:hardware">
                   <interleave>
                    <optional>
                     <element name="dhcp:type">
                      <choice>
                       <value>ethernet</value>
                       <value>token-ring</value>
                       <value>fddi</value>
                      </choice>
                     </element>
                    </optional>
                    <optional>



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                     <element name="dhcp:address">
                      <ref name="ietf-yang-types__phys-address"/>
                     </element>
                    </optional>
                   </interleave>
                  </element>
                 </optional>
                </interleave>
               </element>
              </zeroOrMore>
             </interleave>
            </element>
           </optional>
          </interleave>
         </element>
        </optional>
       </interleave>
      </element>
      <element name="nmt:rpc-methods">
       <empty/>
      </element>
      <element name="nmt:notifications">
       <empty/>
      </element>
     </element>
    </start>
    <define name="_dhcp__subnet-list">
     <interleave>
      <a:documentation>A reusable list of subnets</a:documentation>
      <zeroOrMore>
       <element name="dhcp:subnet" nma:key="dhcp:net">
        <element name="dhcp:net">
         <ref name="ietf-inet-types__ip-prefix"/>
        </element>
        <interleave>
         <optional>
          <element name="dhcp:range">
           <interleave>
            <optional>
             <element name="dhcp:dynamic-bootp">
              <a:documentation>
               Allows BOOTP clients to get addresses in this range
              </a:documentation>
              <empty/>
             </element>
            </optional>
            <element name="dhcp:low">
             <ref name="ietf-inet-types__ip-address"/>



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            </element>
            <element name="dhcp:high">
             <ref name="ietf-inet-types__ip-address"/>
            </element>
           </interleave>
          </element>
         </optional>
         <optional>
          <element name="dhcp:dhcp-options">
           <interleave>
            <a:documentation>
             Options in the DHCP protocol
            </a:documentation>
            <zeroOrMore>
             <element name="dhcp:router" nma:ordered-by="user">
              <a:documentation>
               See: RFC 2132, sec. 3.8
              </a:documentation>
              <ref name="ietf-inet-types__host"/>
             </element>
            </zeroOrMore>
            <optional>
             <element name="dhcp:domain-name">
              <a:documentation>
               See: RFC 2132, sec. 3.17
              </a:documentation>
              <ref name="ietf-inet-types__domain-name"/>
             </element>
            </optional>
           </interleave>
          </element>
         </optional>
         <optional>
          <element name="dhcp:max-lease-time"
                   nma:default="7200" nma:units="seconds">
           <data type="unsignedInt"/>
          </element>
         </optional>
        </interleave>
       </element>
      </zeroOrMore>
     </interleave>
    </define>
    <define name="ietf-inet-types__ip-prefix">
     <choice>
      <ref name="ietf-inet-types__ipv4-prefix"/>
      <ref name="ietf-inet-types__ipv6-prefix"/>
     </choice>



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    </define>
    <define name="ietf-inet-types__ipv4-prefix">
     <data type="string">
      <param name="pattern">... regex pattern ...</param>
     </data>
    </define>
    <define name="ietf-inet-types__ipv6-prefix">
     <data type="string">
      <param name="pattern">... regex pattern ...</param>
      <param name="pattern">... regex pattern ...</param>
     </data>
    </define>
    <define name="ietf-inet-types__ip-address">
     <choice>
      <ref name="ietf-inet-types__ipv4-address"/>
      <ref name="ietf-inet-types__ipv6-address"/>
     </choice>
    </define>
    <define name="ietf-inet-types__ipv4-address">
     <data type="string">
      <param name="pattern">... regex pattern ...</param>
     </data>
    </define>
    <define name="ietf-inet-types__ipv6-address">
     <data type="string">
      <param name="pattern">... regex pattern ...</param>
      <param name="pattern">... regex pattern ...</param>
     </data>
    </define>
    <define name="ietf-inet-types__host">
     <choice>
      <ref name="ietf-inet-types__ip-address"/>
      <ref name="ietf-inet-types__domain-name"/>
     </choice>
    </define>
    <define name="ietf-inet-types__domain-name">
     <data type="string">
      <param name="minLength">1</param>
      <param name="maxLength">253</param>
      <param name="pattern">... regex pattern ...</param>
     </data>
    </define>
    <define name="ietf-yang-types__date-and-time">
     <data type="string">
      <param name="pattern">... regex pattern ...</param>
     </data>
    </define>
    <define name="ietf-yang-types__phys-address">



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     <data type="string">
      <param name="pattern">
       ([0-9a0-fA-F]{2}(:[0-9a0-fA-F]{2})*)?
      </param>
     </data>
    </define>
   </grammar>

C.2.2.  Compact Syntax

  namespace a = "http://relaxng.org/ns/compatibility/annotations/1.0"
  namespace dc = "http://purl.org/dc/terms"
  namespace dhcp = "http://example.com/ns/dhcp"
  namespace nma = "urn:ietf:params:xml:ns:netmod:dsdl-annotations:1"
  namespace nmt = "urn:ietf:params:xml:ns:netmod:conceptual-tree:1"

  dc:creator [ "Pyang 0.9.3, CTS plugin" ]
  dc:source [ "YANG module 'dhcp'" ]
  start =
   element nmt:netmod-tree {
    element nmt:top {
     [ nma:implicit = "true" ]
     element dhcp:dhcp {

      ##
      ##   configuration and operational parameters for a DHCP server
      ##
      ([ nma:default = "7200" nma:units = "seconds" ]
       element dhcp:max-lease-time { xsd:unsignedInt }?
       & [ nma:default = "600" nma:units = "seconds" ]
        element dhcp:default-lease-time {
         xsd:unsignedInt
         >> nma:must [
           assert = ". <= ../dhcp:max-lease-time"
           nma:error-message [
            "\x{a}" ~
            "The default-lease-time must be less than max-lease-time." ~
            "\x{a}"
           ]
          ]
        }?
       & _dhcp__subnet-list
       & element dhcp:shared-networks {
         [ nma:key = "dhcp:name" ]
         element dhcp:shared-network {
          element dhcp:name { xsd:string },
          (_dhcp__subnet-list)
         }*



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        }?
       & [ nma:config = "false" ]
        element dhcp:status {
         [ nma:key = "dhcp:address" ]
         element dhcp:leases {
          element dhcp:address { ietf-inet-types__ip-address },
          (element dhcp:starts { ietf-yang-types__date-and-time }?
          & element dhcp:ends { ietf-yang-types__date-and-time }?
          & element dhcp:hardware {
            element dhcp:type {
             "ethernet" | "token-ring" | "fddi"
            }?
            & element dhcp:address {
              ietf-yang-types__phys-address
             }?
           }?)
         }*
        }?)
     }?
    },
    element nmt:rpc-methods { empty },
    element nmt:notifications { empty }
   }
  _dhcp__subnet-list =

   ## A reusable list of subnets
   ([ nma:key = "dhcp:net" ]
    element dhcp:subnet {
     element dhcp:net { ietf-inet-types__ip-prefix },
     (element dhcp:range {

      ##
      ##      Allows BOOTP clients to get addresses in this range
      ##
      element dhcp:dynamic-bootp { empty }?
      & element dhcp:low { ietf-inet-types__ip-address }
      & element dhcp:high { ietf-inet-types__ip-address }
     }?
     & element dhcp:dhcp-options {

       ##
       ##   Options in the DHCP protocol
       ##
       (
        ##
        ##            See: RFC 2132, sec. 3.8
        ##
        [ nma:ordered-by = "user" ]



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        element dhcp:router { ietf-inet-types__host }*
        &
         ##
         ##           See: RFC 2132, sec. 3.17
         ##
         element dhcp:domain-name { ietf-inet-types__domain-name }?)
      }?
     & [ nma:default = "7200" nma:units = "seconds" ]
      element dhcp:max-lease-time { xsd:unsignedInt }?)
    }*)
  ietf-inet-types__ip-prefix =
   ietf-inet-types__ipv4-prefix | ietf-inet-types__ipv6-prefix
  ietf-inet-types__ipv4-prefix =
   xsd:string { pattern = "... regex pattern ..." }
  ietf-inet-types__ipv6-prefix =
   xsd:string {
    pattern = "... regex pattern ..."
    pattern = "... regex pattern ..."
   }
  ietf-inet-types__ip-address =
   ietf-inet-types__ipv4-address | ietf-inet-types__ipv6-address
  ietf-inet-types__ipv4-address =
   xsd:string { pattern = "... regex pattern ..." }
  ietf-inet-types__ipv6-address =
   xsd:string {
    pattern = "... regex pattern ..."
    pattern = "... regex pattern ..."
   }
  ietf-inet-types__host =
   ietf-inet-types__ip-address | ietf-inet-types__domain-name
  ietf-inet-types__domain-name =
   xsd:string {
    minLength = "1"
    maxLength = "253"
    pattern = "... regex pattern ..."
   }
  ietf-yang-types__date-and-time =
   xsd:string { pattern = "... regex pattern ..." }
  ietf-yang-types__phys-address =
   xsd:string {
    pattern = "([0-9a0-fA-F]{2}(:[0-9a0-fA-F]{2})*)?"
   }

C.3.  Final DSDL Schemas

   This appendix contains DSDL schemas that were obtained from the
   conceptual tree schema in Appendix C.2 by XSL transformations.  These
   schemas can be directly used for validating a reply to unfiltered



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   <get> with the contents corresponding to the DHCP data model.

   The RELAX NG schema (again shown in both XML and compact syntax)
   includes the schema independent library from Appendix B.

C.3.1.  RELAX NG Schema for <get> Reply - XML Syntax

   <?xml version="1.0" encoding="utf-8"?>
   <grammar
       xmlns="http://relaxng.org/ns/structure/1.0"
       xmlns:a="http://relaxng.org/ns/compatibility/annotations/1.0"
       xmlns:dc="http://purl.org/dc/terms"
       xmlns:dhcp="http://example.com/ns/dhcp"
       xmlns:nma="urn:ietf:params:xml:ns:netmod:dsdl-annotations:1"
       xmlns:nmt="urn:ietf:params:xml:ns:netmod:conceptual-tree:1"
       datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes"
       ns="urn:ietf:params:xml:ns:netconf:base:1.0">
    <include href="relaxng-lib.rng"/>
    <start>
     <element name="rpc-reply">
      <ref name="message-id-attribute"/>
      <element name="data">
       <interleave>
        <optional>
         <element name="dhcp:dhcp">
          <interleave>
           <optional>
            <element name="dhcp:max-lease-time">
             <data type="unsignedInt"/>
            </element>
           </optional>
           <optional>
            <element name="dhcp:default-lease-time">
             <data type="unsignedInt"/>
            </element>
           </optional>
           <ref name="_dhcp__subnet-list"/>
           <optional>
            <element name="dhcp:shared-networks">
             <interleave>
              <zeroOrMore>
               <element name="dhcp:shared-network">
                <element name="dhcp:name">
                 <data type="string"/>
                </element>
                <interleave>
                 <ref name="_dhcp__subnet-list"/>
                </interleave>



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               </element>
              </zeroOrMore>
             </interleave>
            </element>
           </optional>
           <optional>
            <element name="dhcp:status">
             <interleave>
              <zeroOrMore>
               <element name="dhcp:leases">
                <element name="dhcp:address">
                 <ref name="ietf-inet-types__ip-address"/>
                </element>
                <interleave>
                 <optional>
                  <element name="dhcp:starts">
                   <ref name="ietf-yang-types__date-and-time"/>
                  </element>
                 </optional>
                 <optional>
                  <element name="dhcp:ends">
                   <ref name="ietf-yang-types__date-and-time"/>
                  </element>
                 </optional>
                 <optional>
                  <element name="dhcp:hardware">
                   <interleave>
                    <optional>
                     <element name="dhcp:type">
                      <choice>
                       <value>ethernet</value>
                       <value>token-ring</value>
                       <value>fddi</value>
                      </choice>
                     </element>
                    </optional>
                    <optional>
                     <element name="dhcp:address">
                      <ref name="ietf-yang-types__phys-address"/>
                     </element>
                    </optional>
                   </interleave>
                  </element>
                 </optional>
                </interleave>
               </element>
              </zeroOrMore>
             </interleave>



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            </element>
           </optional>
          </interleave>
         </element>
        </optional>
       </interleave>
      </element>
     </element>
    </start>
    <define name="_dhcp__subnet-list">
     <interleave>
      <zeroOrMore>
       <element name="dhcp:subnet">
        <element name="dhcp:net">
         <ref name="ietf-inet-types__ip-prefix"/>
        </element>
        <interleave>
         <optional>
          <element name="dhcp:range">
           <interleave>
            <optional>
             <element name="dhcp:dynamic-bootp">
              <empty/>
             </element>
            </optional>
            <element name="dhcp:low">
             <ref name="ietf-inet-types__ip-address"/>
            </element>
            <element name="dhcp:high">
             <ref name="ietf-inet-types__ip-address"/>
            </element>
           </interleave>
          </element>
         </optional>
         <optional>
          <element name="dhcp:dhcp-options">
           <interleave>
            <zeroOrMore>
             <element name="dhcp:router">
              <ref name="ietf-inet-types__host"/>
             </element>
            </zeroOrMore>
            <optional>
             <element name="dhcp:domain-name">
              <ref name="ietf-inet-types__domain-name"/>
             </element>
            </optional>
           </interleave>



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          </element>
         </optional>
         <optional>
          <element name="dhcp:max-lease-time">
           <data type="unsignedInt"/>
          </element>
         </optional>
        </interleave>
       </element>
      </zeroOrMore>
     </interleave>
    </define>
    <define name="ietf-inet-types__ip-prefix">
     <choice>
      <ref name="ietf-inet-types__ipv4-prefix"/>
      <ref name="ietf-inet-types__ipv6-prefix"/>
     </choice>
    </define>
    <define name="ietf-inet-types__ipv4-prefix">
     <data type="string">
      <param name="pattern">... regex pattern ...</param>
     </data>
    </define>
    <define name="ietf-inet-types__ipv6-prefix">
     <data type="string">
      <param name="pattern">... regex pattern ...</param>
      <param name="pattern">... regex pattern ...</param>
     </data>
    </define>
    <define name="ietf-inet-types__ip-address">
     <choice>
      <ref name="ietf-inet-types__ipv4-address"/>
      <ref name="ietf-inet-types__ipv6-address"/>
     </choice>
    </define>
    <define name="ietf-inet-types__ipv4-address">
     <data type="string">
      <param name="pattern">... regex pattern ...</param>
     </data>
    </define>
    <define name="ietf-inet-types__ipv6-address">
     <data type="string">
      <param name="pattern">... regex pattern ...</param>
      <param name="pattern">... regex pattern ...</param>
     </data>
    </define>
    <define name="ietf-inet-types__host">
     <choice>



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      <ref name="ietf-inet-types__ip-address"/>
      <ref name="ietf-inet-types__domain-name"/>
     </choice>
    </define>
    <define name="ietf-inet-types__domain-name">
     <data type="string">
      <param name="minLength">1</param>
      <param name="maxLength">253</param>
      <param name="pattern">... regex pattern ...</param>
     </data>
    </define>
    <define name="ietf-yang-types__date-and-time">
     <data type="string">
      <param name="pattern">... regex pattern ...</param>
     </data>
    </define>
    <define name="ietf-yang-types__phys-address">
     <data type="string">
      <param name="pattern">
       ([0-9a0-fA-F]{2}(:[0-9a0-fA-F]{2})*)?
      </param>
     </data>
    </define>
   </grammar>

C.3.2.  RELAX NG Schema for <get> Reply - Compact Syntax

  default namespace = "urn:ietf:params:xml:ns:netconf:base:1.0"
  namespace a = "http://relaxng.org/ns/compatibility/annotations/1.0"
  namespace dc = "http://purl.org/dc/terms"
  namespace dhcp = "http://example.com/ns/dhcp"
  namespace nma = "urn:ietf:params:xml:ns:netmod:dsdl-annotations:1"
  namespace nmt = "urn:ietf:params:xml:ns:netmod:conceptual-tree:1"

  include "relaxng-lib.rnc"
  start =
    element rpc-reply {
      message-id-attribute,
      element data {
        element dhcp:dhcp {
          element dhcp:max-lease-time { xsd:unsignedInt }?
          & element dhcp:default-lease-time { xsd:unsignedInt }?
          & _dhcp__subnet-list
          & element dhcp:shared-networks {
              element dhcp:shared-network {
                element dhcp:name { xsd:string },
                (_dhcp__subnet-list)
              }*



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            }?
          & element dhcp:status {
              element dhcp:leases {
                element dhcp:address { ietf-inet-types__ip-address },
                (element dhcp:starts { ietf-yang-types__date-and-time }?
                 & element dhcp:ends { ietf-yang-types__date-and-time }?
                 & element dhcp:hardware {
                     element dhcp:type {
                       "ethernet" | "token-ring" | "fddi"
                     }?
                     & element dhcp:address {
                         ietf-yang-types__phys-address
                       }?
                   }?)
              }*
            }?
        }?
      }
    }
  _dhcp__subnet-list =
    element dhcp:subnet {
      element dhcp:net { ietf-inet-types__ip-prefix },
      (element dhcp:range {
         element dhcp:dynamic-bootp { empty }?
         & element dhcp:low { ietf-inet-types__ip-address }
         & element dhcp:high { ietf-inet-types__ip-address }
       }?
       & element dhcp:dhcp-options {
           element dhcp:router { ietf-inet-types__host }*
           & element dhcp:domain-name { ietf-inet-types__domain-name }?
         }?
       & element dhcp:max-lease-time { xsd:unsignedInt }?)
    }*
  ietf-inet-types__ip-prefix =
    ietf-inet-types__ipv4-prefix | ietf-inet-types__ipv6-prefix
  ietf-inet-types__ipv4-prefix =
    xsd:string { pattern = "... regex pattern ..." }
  ietf-inet-types__ipv6-prefix =
    xsd:string {
      pattern = "... regex pattern ..."
      pattern = "... regex pattern ..."
    }
  ietf-inet-types__ip-address =
    ietf-inet-types__ipv4-address | ietf-inet-types__ipv6-address
  ietf-inet-types__ipv4-address =
    xsd:string { pattern = "... regex pattern ..." }
  ietf-inet-types__ipv6-address =
    xsd:string {



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      pattern = "... regex pattern ..."
      pattern = "... regex pattern ..."
    }
  ietf-inet-types__host =
    ietf-inet-types__ip-address | ietf-inet-types__domain-name
  ietf-inet-types__domain-name =
    xsd:string {
      minLength = "1"
      maxLength = "253"
      pattern = "... regex pattern ..."
    }
  ietf-yang-types__date-and-time =
    xsd:string { pattern = "... regex pattern ..." }
  ietf-yang-types__phys-address =
    xsd:string {
      pattern =
        "\x{a}" ~
        "    ([0-9a0-fA-F]{2}(:[0-9a0-fA-F]{2})*)?\x{a}" ~
        "   "
    }

C.4.  Schematron Schema for <get> Reply

   <?xml version="1.0" encoding="utf-8"?>
   <sch:schema xmlns:sch="http://purl.oclc.org/dsdl/schematron">
     <sch:ns uri="http://example.com/ns/dhcp" prefix="dhcp"/>
     <sch:ns uri="urn:ietf:params:xml:ns:netconf:base:1.0"
             prefix="nc"/>
     <sch:phase id="full">
       <sch:active pattern="standard"/>
       <sch:active pattern="ref-integrity"/>
     </sch:phase>
     <sch:phase id="noref">
       <sch:active pattern="standard"/>
     </sch:phase>
     <sch:pattern id="standard">
       <sch:rule id="std-id2247270" abstract="true">
         <sch:report test="preceding-sibling::dhcp:subnet
                           [dhcp:net=current()/dhcp:net]">
         Duplicate key of list dhcp:subnet
         </sch:report>
       </sch:rule>
       <sch:rule context="/nc:rpc-reply/nc:data/dhcp:dhcp/
                          dhcp:default-lease-time">
         <sch:assert test=". &lt;= ../dhcp:max-lease-time">
           The default-lease-time must be less than max-lease-time.
         </sch:assert>
       </sch:rule>



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       <sch:rule context="/nc:rpc-reply/nc:data/dhcp:dhcp/dhcp:subnet">
         <sch:extends rule="std-id2247270"/>
       </sch:rule>
       <sch:rule context="/nc:rpc-reply/nc:data/dhcp:dhcp/
                          dhcp:shared-networks/dhcp:shared-network">
         <sch:report test="preceding-sibling::dhcp:shared-network
                           [dhcp:name=current()/dhcp:name]">
           Duplicate key of list dhcp:shared-network
         </sch:report>
       </sch:rule>
       <sch:rule context="/nc:rpc-reply/nc:data/dhcp:dhcp/
                          dhcp:shared-networks/dhcp:shared-network/
                          dhcp:subnet">
         <sch:extends rule="std-id2247270"/>
       </sch:rule>
       <sch:rule context="/nc:rpc-reply/nc:data/dhcp:dhcp/
                          dhcp:status/dhcp:leases">
         <sch:report test="preceding-sibling::dhcp:leases
                           [dhcp:address=current()/dhcp:address]">
           Duplicate key of list dhcp:leases
         </sch:report>
       </sch:rule>
     </sch:pattern>
     <sch:pattern id="ref-integrity"/>
   </sch:schema>


























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C.5.  DSRL Schema for <get> Reply

   <?xml version="1.0" encoding="utf-8"?>
   <dsrl:maps xmlns:dsrl="http://purl.oclc.org/dsdl/dsrl"
              xmlns:dhcp="http://example.com/ns/dhcp"
              xmlns:nc="urn:ietf:params:xml:ns:netconf:base:1.0">
     <dsrl:element-map>
       <dsrl:parent>/nc:rpc-reply/nc:data/</dsrl:parent>
       <dsrl:name>dhcp:dhcp</dsrl:name>
       <dsrl:default-content>
         <dhcp:max-lease-time>7200</dhcp:max-lease-time>
         <dhcp:default-lease-time>600</dhcp:default-lease-time>
       </dsrl:default-content>
     </dsrl:element-map>
     <dsrl:element-map>
       <dsrl:parent>/nc:rpc-reply/nc:data/dhcp:dhcp</dsrl:parent>
       <dsrl:name>dhcp:max-lease-time</dsrl:name>
       <dsrl:default-content>7200</dsrl:default-content>
     </dsrl:element-map>
     <dsrl:element-map>
       <dsrl:parent>/nc:rpc-reply/nc:data/dhcp:dhcp</dsrl:parent>
       <dsrl:name>dhcp:default-lease-time</dsrl:name>
       <dsrl:default-content>600</dsrl:default-content>
     </dsrl:element-map>
     <dsrl:element-map>
       <dsrl:parent>
         /nc:rpc-reply/nc:data/dhcp:dhcp/dhcp:subnet
       </dsrl:parent>
       <dsrl:name>dhcp:max-lease-time</dsrl:name>
       <dsrl:default-content>7200</dsrl:default-content>
     </dsrl:element-map>
     <dsrl:element-map>
       <dsrl:parent>
         /nc:rpc-reply/nc:data/dhcp:dhcp/dhcp:shared-networks/
         dhcp:shared-network/dhcp:subnet
       </dsrl:parent>
       <dsrl:name>dhcp:max-lease-time</dsrl:name>
       <dsrl:default-content>7200</dsrl:default-content>
     </dsrl:element-map>
   </dsrl:maps>











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Appendix D.  Change Log

D.1.  Changes Between Versions -04 and -05

   o  Leafs that take their default value from a typedef and are not
      annotated with @nma:default must have @nma:implicit="true".

   o  Changed code markers CODE BEGINS/ENDS to the form agreed by the
      WG.

   o  Derived types "date-and-time" and "uri" SHOULD be mapped to XSD
      "dateTime" and "anyURI" types, respectively.

   o  Clarified the notion of implicit nodes under under 'case' in
      Section 9.1.2.

   o  Moved draft-ietf-netmod-yang-types-06 to normative references.

   o  An extra <rng:group> is no more required for the default case of a
      choice in the shorthand notation.

D.2.  Changes Between Versions -03 and -04

   o  Implemented ordering rules for list children - keys must go first
      and appear in the same order as in the input YANG module.

   o  The 'case' statement is now mapped to either <rng:group> (inside
      RPCs) or <rng:interleave> (otherwise).

   o  A nma:default annotation coming from a datatype which the mapping
      expands is attached to the <rng:element> pattern where the
      expansion occurs.  Added an example.

   o  Documentation statements ('description', 'reference', 'status')
      MAY be ignored.

   o  Single-valued numeric or length range parts are mapped to <rng:
      value> pattern or "length" facet.

   o  Example for "string" datatype was added.

   o  Appendix A now uses NVDL for defining NETMOD-specific annotations.

   o  Added CODE BEGINS/ENDS markers.

   o  Separated normative and informative references.





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   o  Added URL for XPath extensions namespace.

   o  Added Section 2 (Terminology and Notation).

   o  Added Section 14 (Security Considerations).

   o  Added Section 15 (Acknowledgments).

   o  Removed compact syntax schema from Appendix B.

   o  Editorial changes: symbolic citation labels.

D.3.  Changes Between Versions -02 and -03

   o  Changed @nma:default-case to @nma:implicit.

   o  Changed nma:leafref annotation from element to attribute.

   o  Added skeleton rule to Section 10.2.

   o  Reworked Section 10.4, added skeleton element maps,corrected the
      example.

   o  Added Section 8.5 on 'feature' and 'deviation'.

   o  New Section 9.1 integrating discussion of both optional/mandatory
      (was in -02) and implicit nodes (new).

   o  Reflected that key argument and schema node identifiers are no
      more XPath (should be in yang-07).

   o  Element patterns for implicit containers now must have @nma:
      implicit attribute.

   o  Removed "float32" and "float64" types and added mapping of
      "decimal64" with example.

   o  Removed mapping of 'require-instance' for "leafref" type.

   o  Updated RELAX NG schema for NETMOD-specific annotations.

   o  Updated the DHCP example.

D.4.  Changes Between Versions -01 and -02

   o  Moved Section 7 "NETCONF Content Validation" after Section 6.





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   o  New text about mapping defaults to DSRL, especially in Section 7
      and Section 10.4.

   o  Finished the DHCP example by adding the DSRL schema to Appendix C.

   o  New @nma:presence annotation was added - it is needed for proper
      handling of default content.

   o  Section 10.3 "Constraints on Mandatory Choice" was added because
      these constraints require a combination of RELAX NG and
      Schematron.

   o  Fixed the schema for NETMOD-specific annotations by adding
      explicit prefix to all defined elements and attributes.
      Previously, the attributes had no namespace.

   o  Handling of 'feature', 'if-feature' and 'deviation' added.

   o  Handling of nma:instance-identifier via XSLT extension function.

D.5.  Changes Between Versions -00 and -01

   o  Attributes @nma:min-elements and @nma:max-elements are attached to
      <rng:element> (list entry) and not to <rng:zeroOrMore> or <rng:
      oneOrMore>.

   o  Keys and all node identifiers in 'key' and 'unique' statements are
      prefixed.

   o  Fixed the mapping of 'rpc' and 'notification'.

   o  Removed previous sec. 7.5 "RPC Signatures and Notifications" - the
      same information is now contained in Section 11.50 and
      Section 11.37.

   o  Added initial "_" to mangled names of groupings.

   o  Mandated the use of @xmlns:xxx as the only method for declaring
      the target namespace.

   o  Added section "Handling of XML Namespaces" to explain the previous
      item.

   o  Completed DHCP example in Appendix C.

   o  Almost all text about the second mapping step is new.





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Authors' Addresses

   Ladislav Lhotka
   CESNET

   Email: lhotka@cesnet.cz


   Rohan Mahy
   Plantronics

   Email: rohan@ekabal.com


   Sharon Chisholm
   Nortel

   Email: schishol@nortel.com

































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