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Versions: (draft-bierman-netmod-yang-data-ext) 00 01 02 03 04 05

Network Working Group                                         A. Bierman
Internet-Draft                                                 YumaWorks
Updates: 8340 (if approved)                                 M. Bjorklund
Intended status: Standards Track                                   Cisco
Expires: January 16, 2020                                      K. Watsen
                                                         Watsen Networks
                                                           July 15, 2019


                     YANG Data Structure Extensions
                   draft-ietf-netmod-yang-data-ext-04

Abstract

   This document describes YANG mechanisms for defining abstract data
   structures with YANG.

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 https://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 January 16, 2020.

Copyright Notice

   Copyright (c) 2019 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
   (https://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 Simplified BSD License.



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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
       1.1.1.  NMDA  . . . . . . . . . . . . . . . . . . . . . . . .   3
       1.1.2.  YANG  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Definitions . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  YANG Data Structures in YANG Tree Diagrams  . . . . . . . . .   4
   4.  YANG Data Structure Extensions Module . . . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
     5.1.  YANG Module Registry  . . . . . . . . . . . . . . . . . .   9
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . .  11
     A.1.  "structure" Example . . . . . . . . . . . . . . . . . . .  11
     A.2.  "augment-structure" Example . . . . . . . . . . . . . . .  13
     A.3.  XML Encoding Example  . . . . . . . . . . . . . . . . . .  13
     A.4.  JSON Encoding Example . . . . . . . . . . . . . . . . . .  14
     A.5.  "structure" example that defines a non-top-level
           structure . . . . . . . . . . . . . . . . . . . . . . . .  14
   Appendix B.  Change Log . . . . . . . . . . . . . . . . . . . . .  15
     B.1.  v02 to v03  . . . . . . . . . . . . . . . . . . . . . . .  15
     B.2.  v01 to v02  . . . . . . . . . . . . . . . . . . . . . . .  15
     B.3.  v00 to v01  . . . . . . . . . . . . . . . . . . . . . . .  15
   Appendix C.  Open Issues  . . . . . . . . . . . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

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] was defined for this purpose but it is limited in its
   functionality.

   The intended use of the "yang-data" extension was to model all or
   part of a protocol message, such as the "errors" definition in the
   YANG module "ietf-restconf" [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.

   The "yang-data" extension from [RFC8040] has been copied here,
   renamed to "structure", and updated to be more flexible.  There is no




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   assumption that a YANG data structure can only be used as a top-level
   abstraction, instead of nested within some other data structure.

   This document also defines a new YANG extension statement called
   "augment-structure", 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 "structure" extension.

1.1.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   The following terms are used within this document:

   o  YANG data structure: A data structure defined with the "structure"
      statement.

1.1.1.  NMDA

   The following terms are defined in the Network Management Datastore
   Architecture (NMDA) [RFC8342].  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




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   o  list

2.  Definitions

   A YANG Data Structure is defined with the "structure" extension
   statement, defined in the YANG module "ietf-yang-structure-ext".  The
   argument to the "structure" extension statement is the name of the
   data structure.  The data structures 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 data structures defined with the "structure"
   statement cannot have the same name as sibling nodes from regular
   YANG data definition statements or other "structure" statements in
   the same YANG module.

   This does not mean a YANG data structure has to be used as a top-
   level protocol message or other top-level data structure.

3.  YANG Data Structures in YANG Tree Diagrams

   A YANG Data Structure can be printed in a YANG Tree Diagram
   [RFC8340].  This document updates RFC 8340 by defining two new
   sections in the tree diagram for a module:

   1.  YANG data structures, offset by two spaces and identified by the
       keyword "structure" followed by the name of the YANG data
       structure and a colon (":") character.

   2.  YANG data structure augmentations, offset by 2 spaces and
       identified by the keyword "augment-structure" followed by the
       augment target structure name and a colon (":") character.

   The new sections, including spaces conventions is:












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       structure <structure-name>:
         +--<node>
            +--<node>
            |  +--<node>
            +--<node>
       structure <structure-name>:
         +--<node>

       augment-structure <structure-name>:
         +--<node>
            +--<node>
            |  +--<node>
            +--<node>
       augment-structure <structure-name>:
         +--<node>

4.  YANG Data Structure Extensions Module

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

   <CODE BEGINS> file "ietf-yang-structure-ext@2019-03-07.yang"

   module ietf-yang-structure-ext {
     yang-version 1.1;
     namespace "urn:ietf:params:xml:ns:yang:ietf-yang-structure-ext";
     prefix sx;

     organization
       "IETF NETMOD (NETCONF Data Modeling Language) Working Group";
     contact
       "WG Web:   <http://tools.ietf.org/wg/netmod/>
        WG List:  <mailto:netmod@ietf.org>

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

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

        Author:   Kent Watsen
                  <mailto:kent+ietf@watsen.net>";
     description
       "This module contains conceptual YANG specifications for defining
        abstract data structures.

        The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL
        NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'NOT RECOMMENDED',



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        'MAY', and 'OPTIONAL' in this document are to be interpreted as
        described in BCP 14 (RFC 2119) (RFC 8174) when, and only when,
        they appear in all capitals, as shown here.

        Copyright (c) 2019 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).";

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

     revision 2019-03-07 {
       description
         "Initial revision.";
       // RFC Ed.: replace XXXX with RFC number and remove this note
       reference
         "RFC XXXX: YANG Structure Extensions.";
     }

     extension structure {
       argument name {
         yin-element true;
       }
       description
         "This extension is used to specify a YANG data structure that
          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 'structure' extension statement specify the generic
          syntax for the specific YANG data structure, whose name is the
          argument of the 'structure' extension statement.

          Note that this extension does not define a media-type.  A
          specification using this extension MUST specify the message
          encoding rules, including the content media type, if
          applicable.

          The mandatory 'name' parameter value identifies the YANG data
          structure that is being defined.

          This extension is only valid as a top-level statement, i.e.,
          given as a sub-statement to 'module' or 'submodule'.



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          The sub-statements of this extension MUST follow the ABNF
          rules below, where the rules are defined in RFC 7950:

            *must-stmt
            [status-stmt]
            [description-stmt]
            [reference-stmt]
            *(typedef-stmt / grouping-stmt)
            *data-def-stmt

          A YANG data structure defined with this extension statement is
          encoded in the same way as an 'anydata' statement.  This means
          that the name of the structure is encoded as a 'container',
          with the instantiated child statements encoded as child nodes
          to this node.

          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 structure.

          The XPath document element is the extension statement itself,
          such that the child nodes of the document element 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 'structure' extension statement.

            - The list-stmt is not required to have a key-stmt defined.
            - The config-stmt is ignored if present.
         ";
     }

     extension augment-structure {
       argument path {
         yin-element true;
       }



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       description
         "This extension is used to specify an augmentation to YANG data
          structure defined with the 'structure' 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
          structure, 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, where the first node in the
          absolute-schema-nodeid string identifies the YANG data
          structure to augment, and the rest of the nodes in the string
          identifies the node within the YANG structure to augment.

          This extension is only valid as a top-level statement, i.e.,
          given as a sub-statement to 'module' or 'submodule'.

          The sub-statements of this extension MUST follow the ABNF
          rules below, where the rules are defined in RFC 7950:

            [status-stmt]
            [description-stmt]
            [reference-stmt]
            1*(data-def-stmt / case-stmt)

          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 element is the augmented extension
          statement itself, such that the child nodes of the document
          element are represented by the data-def-stmt sub-statements
          within the augmented 'structure' statement.

          The context node of the 'augment-structure' statement is
          derived in the same way as the 'augment' statement, as defined
          in section 6.4.1 of [RFC7950]. This conceptual node is
          considered the context node for the following YANG statements:

            - must-stmt
            - when-stmt
            - path-stmt



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            - 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 an 'augment-structure' extension statement.

            - The list-stmt is not required to have a key-stmt defined.
            - The config-stmt is ignored if present.

          Example:

             module foo {
                import ietf-yang-structure-ext { prefix sx; }

                sx:structure foo-data {
                  container foo-con { }
                }
             }

             module bar {
                import ietf-yang-structure-ext { prefix sx; }
                import foo { prefix foo; }

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

   <CODE ENDS>

5.  IANA Considerations

5.1.  YANG Module Registry

   This document registers one URI as a namespace in the "IETF XML
   Registry" [RFC3688]:

       URI: urn:ietf:params:xml:ns:yang:ietf-yang-structure-ext
       Registrant Contact: The IESG.
       XML: N/A; the requested URI is an XML namespace.



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   This document registers one YANG module in the "YANG Module Names"
   registry [RFC6020]:

       name:         ietf-yang-structure-ext
       namespace:    urn:ietf:params:xml:ns:yang:ietf-yang-structure-ext
       prefix:       sx
       // RFC Ed.: replace XXXX with RFC number and remove this note
       reference:    RFC XXXX

6.  Security Considerations

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

7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

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

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

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8340]  Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
              BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
              <https://www.rfc-editor.org/info/rfc8340>.

   [RFC8342]  Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
              and R. Wilton, "Network Management Datastore Architecture
              (NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018,
              <https://www.rfc-editor.org/info/rfc8342>.







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7.2.  Informative References

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,
              <https://www.rfc-editor.org/info/rfc3688>.

   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,
              <https://www.rfc-editor.org/info/rfc6020>.

7.3.  URIs

   [1] https://github.com/netmod-wg/yang-data-ext/issues

Appendix A.  Examples

A.1.  "structure" Example

   This example shows a simple address book that could be stored as an
   artifact.






























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   module example-module {
     yang-version 1.1;
     namespace "urn:example:example-module";
     prefix exm;

     import ietf-yang-structure-ext {
       prefix sx;
     }

     sx:structure address-book {
       list address {
         key "last first";
         leaf last {
           type string;
           description "Last name";
         }
         leaf first {
           type string;
           description "First name";
         }
         leaf street {
           type string;
           description "Street name";
         }
         leaf city {
           type string;
           description "City name";
         }
         leaf state {
           type string;
           description "State name";
         }
       }
     }
   }


   Below is the tree diagram of this module.

   module: example-module

     structure address-book:
       +-- address* [last first]
          +-- last      string
          +-- first     string
          +-- street?   string
          +-- city?     string
          +-- state?    string



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A.2.  "augment-structure" Example

   This example adds "county" and "zipcode" leafs to the address book:

   module example-module-aug {
     yang-version 1.1;
     namespace "urn:example:example-module-aug";
     prefix exma;

     import ietf-yang-structure-ext {
       prefix sx;
     }
     import example-module {
       prefix exm;
     }

     sx:augment-structure "/exm:address-book/exm:address" {
       leaf county {
         type string;
         description "County name";
       }
       leaf zipcode {
         type string;
         description "Postal zipcode";
       }
     }
   }


   Below is the tree diagram of this module.

   module: example-module-aug

     augment-structure /exm:address-book/exm:address:
       +-- county?    string
       +-- zipcode?   string

A.3.  XML Encoding Example

   This example shows how an address book can be encoded in XML:











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   <address-book xmlns="urn:example:example-module">
     <address>
       <last>Flintstone</last>
       <first>Fred</first>
       <street>301 Cobblestone Way</street>
       <city>Bedrock</city>
       <zipcode xmlns="urn:example:example-module-aug">70777</zipcode>
     </address>
   </address-book>

A.4.  JSON Encoding Example

   This example shows how an address book can be encoded in JSON:

   "example-module:address-book": {
     "address": [
       {
         "city": "Bedrock",
         "example-module-aug:zipcode": "70777",
         "first": "Fred",
         "last": "Flintstone",
         "street": "301 Cobblestone Way"
       }
     ]
   }

A.5.  "structure" example that defines a non-top-level structure

   The following example defines a data structure with error
   information, that can be included in an <error-info> element in an
   <rpc-error>.

   module example-error-info {
     yang-version 1.1;
     namespace "urn:example:example-error-info";
     prefix exei;

     import ietf-yang-structure-ext {
       prefix sx;
     }

     sx:structure my-example-error-info {
       leaf error-code {
         type uint32;
       }
     }

   }



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   The example below shows how this structure can be used in an
   <rpc-error>.

   <rpc-reply message-id="101"
        xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
     <rpc-error>
       <error-type>protocol</error-type>
       <error-tag>operation-failed</error-tag>
       <error-severity>error</error-severity>
       <error-info>
         <my-example-error-info
             xmlns="urn:example:example-error-info">
           <error-code>42</error-code>
         </my-example-error-info>
       </error-info>
     </rpc-error>
   </rpc-reply>

Appendix B.  Change Log

   RFC Ed.: remove this section before publication.

B.1.  v02 to v03

   o  added YANG tree diagram syntax

   o  added more examples

B.2.  v01 to v02

   o  terminology fixes (use the term "structure" instead of "template")

   o  renamed the statement to "structure" from "yang-data"

   o  removed limitations on if-feature and identities in YANG
      structures

B.3.  v00 to v01

   o  moved open issues to github

   o  added examples section

   o  filled in IANA considerations







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Appendix C.  Open Issues

   RFC Ed.: remove this section before publication.

   The YANG Data Structure Extensions issues are tracked on github.com:

   https://github.com/netmod-wg/yang-data-ext/issues [1]

Authors' Addresses

   Andy Bierman
   YumaWorks

   Email: andy@yumaworks.com


   Martin Bjorklund
   Cisco

   Email: mbj@tail-f.com


   Kent Watsen
   Watsen Networks

   Email: kent+ietf@watsen.net

























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