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Versions: 00 01 draft-ietf-netmod-yang-data-ext

Network Working Group                                         A. Bierman
Internet-Draft                                                 YumaWorks
Intended status: Standards Track                            M. Bjorklund
Expires: May 3, 2018                                      Tail-f Systems
                                                               K. Watsen
                                                        Juniper Networks
                                                        October 30, 2017


                          YANG Data Extensions
                 draft-bierman-netmod-yang-data-ext-01

Abstract

   This document describes YANG mechanisms for defining abstract data
   structures with YANG.  It is intended to replace and extend the
   "yang-data" extension statement defined in RFC 8040.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on May 3, 2018.

Copyright Notice

   Copyright (c) 2017 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




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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
       1.1.1.  NMDA  . . . . . . . . . . . . . . . . . . . . . . . .   3
       1.1.2.  YANG  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Definitions . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Restrictions on Conceptual YANG Data  . . . . . . . . . .   4
     2.2.  YANG Data Extensions Module . . . . . . . . . . . . . . .   4
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
     3.1.  YANG Module Registry  . . . . . . . . . . . . . . . . . .   9
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   5.  Normative References  . . . . . . . . . . . . . . . . . . . .   9
   Appendix A.  Change Log . . . . . . . . . . . . . . . . . . . . .   9
     A.1.  v00 to v01  . . . . . . . . . . . . . . . . . . . . . . .   9
   Appendix B.  Open Issues  . . . . . . . . . . . . . . . . . . . .   9
     B.1.  uses-yang-data  . . . . . . . . . . . . . . . . . . . . .  10
     B.2.  error-info  . . . . . . . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   There is a need for standard mechanisms to allow the definition of
   abstract data that is not intended to be implemented as configuration
   or operational state.  The "yang-data" extension statement from RFC
   8040 [RFC8040] is defined for this purpose, however it is limited in
   its functionality.

   The intended use of the "yang-data" extension is to model all or part
   of a protocol message, such as the "errors" definition in ietf-
   restconf.yang [RFC8040], or the contents of a file.  However,
   protocols are often layered such that the header or payload portions
   of the message can be extended by external documents.  The YANG
   statements that model a protocol need to support this extensibility
   that is already found in that protocol.

   This document defines a new YANG extension statement called
   "augment-yang-data", which allows abstract data structures to be
   augmented from external modules, similar to the existing YANG
   "augment" statement.  Note that "augment" cannot be used to augment a
   yang data structure since a YANG compiler or other tool is not
   required to understand the "yang-data" extension.

   The "yang-data" extension from [RFC8040] has been copied here and
   updated to be more flexible.  There is no longer a requirement for



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   the "yang-data" statement to result in exactly one container object.
   There is no longer an assumption that a yang data structure can only
   be used as a top-level abstraction, instead of nested within some
   other data structure.

1.1.  Terminology

   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].

   The following terms are used within this document:

   o  yang data structure: A data structure defined with the "yang-data"
      statement.

1.1.1.  NMDA

   The following terms are defined in the Network Management Datastore
   Architecture (NMDA) [I-D.ietf-netmod-revised-datastores].  and are
   not redefined here:

   o  configuration

   o  operational state

1.1.2.  YANG

   The following terms are defined in [RFC7950]:

   o  absolute-schema-nodeid

   o  container

   o  data definition statement

   o  data node

   o  leaf

   o  leaf-list

   o  list








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2.  Definitions

2.1.  Restrictions on Conceptual YANG Data

   This document places restrictions on the "yang-data" external
   statements that can be used with the "yang-data" and
   "augment-yang-data" extensions.  The conceptual data definitions are
   considered to be in the same identifier namespace as defined in
   section 6.2.1 of [RFC7950].  In particular, bullet 7:

      All leafs, leaf-lists, lists, containers, choices, rpcs, actions,
      notifications, anydatas, and anyxmls defined (directly or through
      a "uses" statement) within a parent node or at the top level of
      the module or its submodules share the same identifier namespace.

   This means that conceptual data defined with the "yang-data" or
   "augment-yang-data" statements cannot have the same local-name as
   sibling nodes from regular YANG data definition statements or other
   "yang-data" or "augment-yang-data" statements.

   This does not mean a yang data structure has to be used as a top-
   level protocol message or other top-level data structure.  A yang
   data structure does not have to result in a single container.

2.2.  YANG Data Extensions Module

   The "yang-data-ext" module defines the "augment-yang-data" extension
   to augment conceptual data already defined with the "yang-data"
   extension.  The RESTCONF "yang-data" extension has been moved to this
   document and updated.

   RFC Ed.: update the date below with the date of RFC publication and
   remove this note.

   <CODE BEGINS> file "yang-data-ext@2017-10-30.yang"

  module yang-data-ext {
    // not assigning real module name and namespace unless
    // and until changed to a draft-ietf-netmod document
    namespace "urn:ietf:params:xml:ns:yang:yang-data-ext";
    prefix "yd";

    organization
      "IETF NETMOD (NETCONF Data Modeling Language) Working Group";

    contact
      "WG Web:   <http://tools.ietf.org/wg/netmod/>
       WG List:  <mailto:netmod@ietf.org>



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       Author:   Andy Bierman
                 <mailto:andy@yumaworks.com>

       Author:   Martin Bjorklund
                 <mailto:mbj@tail-f.com>

       Author:   Kent Watsen
                 <mailto:kwatsen@juniper.net>";


    description
      "This module contains conceptual YANG specifications
       for defining abstract 'yang-data' data structures.

       Copyright (c) 2017 IETF Trust and the persons identified as
       authors of the code.  All rights reserved.

       Redistribution and use in source and binary forms, with or
       without modification, is permitted pursuant to, and subject
       to the license terms contained in, the Simplified BSD License
       set forth in Section 4.c of the IETF Trust's Legal Provisions
       Relating to IETF Documents
       (http://trustee.ietf.org/license-info).";

    revision 2017-10-30 {
      description
        "Initial revision.";
      reference
        "RFC XXXX: YANG Data Extensions.";
    }


    extension yang-data {
      argument name {
        yin-element true;
      }
      description
        "This extension is used to specify a YANG data template which
         represents conceptual data defined in YANG. It is
         intended to describe hierarchical data independent of
         protocol context or specific message encoding format.
         Data definition statements within a yang-data extension
         specify the generic syntax for the specific YANG data
         template, whose name is the argument of the yang-data
         extension statement.

         Note that this extension does not define a media-type.
         A specification using this extension MUST specify the



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         message encoding rules, including the content media type.

         The mandatory 'name' parameter value identifies the YANG
         data template that is being defined. It contains the
         template name. This parameter is only used for readability
         purposes. There are no mechanisms to reuse yang-data by
         its template name value.

         This extension is ignored unless it appears as a top-level
         statement. It MUST contain data definition statements
         that result in a set of data definition statements.

         If the yang data template is intended to be used as
         a top-level structure, then the yang data template needs to
         result in a single container, so an instance of the YANG data
         template can thus be translated into an XML instance document,
         whose top-level element corresponds to the top-level container.

         The module name and namespace value for the YANG module using
         the extension statement is assigned to each of the data
         definition statements resulting from the yang data template.
         The name of each data definition statement resulting from
         a yang data template is assigned to a top-level identifier name
         in the data node identifier namespace, according to RFC 7950,
         section 6.2.1.

         The sub-statements of this extension MUST follow the
         'data-def-stmt' rule in the YANG ABNF.

         The XPath document root is the extension statement itself,
         such that the child nodes of the document root are
         represented by the data-def-stmt sub-statements within
         this extension. This conceptual document is the context
         for the following YANG statements:

           - must-stmt
           - when-stmt
           - path-stmt
           - min-elements-stmt
           - max-elements-stmt
           - mandatory-stmt
           - unique-stmt
           - ordered-by
           - instance-identifier data type

         The following data-def-stmt sub-statements are constrained
         when used within a yang-data-resource extension statement.




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           - The list-stmt is not required to have a key-stmt defined.
           - The if-feature-stmt is ignored if present.
           - The config-stmt is ignored if present.
           - The available identity values for any 'identityref'
             leaf or leaf-list nodes is limited to the module
             containing this extension statement, and the modules
             imported into that module.
        ";
    }


    extension augment-yang-data {
      argument path {
        yin-element true;
      }
      description
        "This extension is used to specify an augmentation to
         conceptual data defined with the 'yang-data' statement.
         It is intended to describe hierarchical data independent
         of protocol context or specific message encoding format.

         This statement has almost the same structure as the
         'augment-stmt'. Data definition statements within this
         statement specify the semantics and generic syntax for the
         additional data to be added to the specific YANG data template,
         identified by the 'path' argument.

         The mandatory 'path' parameter value identifies the YANG
         conceptual data node that is being augmented, represented
         as an absolute-schema-nodeid string.

         This extension is ignored unless it appears as a top-level
         statement. The sub-statements of this extension MUST follow
         the 'data-def-stmt' rule in the YANG ABNF.

         The module name and namespace value for the YANG module using
         the extension statement is assigned to instance document data
         conforming to the data definition statements within
         this extension.

         The XPath document root is the augmented extension statement
         itself, such that the child nodes of the document root are
         represented by the data-def-stmt sub-statements within
         the augmented yang-data statement.

         The context node of the augment-yang-data statement is derived
         in the same way as the 'augment' statement, as defined in
         section 6.4.1 of [RFC7950]. This conceptual node is



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         considered the context node for the following YANG statements:

           - must-stmt
           - when-stmt
           - path-stmt
           - min-elements-stmt
           - max-elements-stmt
           - mandatory-stmt
           - unique-stmt
           - ordered-by
           - instance-identifier data type

         The following data-def-stmt sub-statements are constrained
         when used within a augment-yang-data extension statement.

           - The list-stmt is not required to have a key-stmt defined.
           - The if-feature-stmt is ignored if present.
           - The config-stmt is ignored if present.
           - The available identity values for any 'identityref'
             leaf or leaf-list nodes is limited to the module
             containing this extension statement, and the modules
             imported into that module.

         Example:

            foo.yang {
               import ietf-restconf { prefix rc; }

               rc:yang-data foo-data {
                 container foo-con { }
               }
            }

            bar.yang {
               import yang-data-ext { prefix yd; }
               import foo { prefix foo; }

               yd:augment-yang-data /foo:foo-con {
                 leaf add-leaf1 { type int32; }
                 leaf add-leaf2 { type string; }
               }
            }
        ";
    }

  }

   <CODE ENDS>



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3.  IANA Considerations

3.1.  YANG Module Registry

   TBD

4.  Security Considerations

   This document defines YANG extensions that are used to define
   conceptual YANG data.  It does not introduce any new vulnerabilities
   beyond those specified in YANG 1.1 [RFC7950].

5.  Normative References

   [I-D.ietf-netmod-revised-datastores]
              Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
              and R. Wilton, "Network Management Datastore
              Architecture", draft-ietf-netmod-revised-datastores-05
              (work in progress), October 2017.

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

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,
              <http://www.rfc-editor.org/info/rfc7950>.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
              <http://www.rfc-editor.org/info/rfc8040>.

Appendix A.  Change Log

A.1.  v00 to v01

   o  Added Martin and Kent as authors

   o  Cloned and updated yang-data from RFC 8040

   o  Added text to clarify that yang-data does not have to result in a
      single container

Appendix B.  Open Issues








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B.1.  uses-yang-data

   Is there a need for a separate grouping and uses mechanism for yang-
   data?  Currently only real grouping-stmt and uses-stmt are used.

B.2.  error-info

   Is there a need for a special-purpose extension to define yang-data
   for the contents of the <error-info> node in NETCONF <rpc-error> and
   RESTCONF <errors> responses?  This node is defined with anyxml so
   there is no way for a YANG tool to use real schema nodes, based on
   the RPC operation being requested or the error-app-tag that is being
   returned.

Authors' Addresses

   Andy Bierman
   YumaWorks

   Email: andy@yumaworks.com


   Martin Bjorklund
   Tail-f Systems

   Email: mbj@tail-f.com


   Kent Watsen
   Juniper Networks

   Email: kwatsen@juniper.net



















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