YANG Data Extensions
draft-bierman-netmod-yang-data-ext-00

Network Working Group                                         A. Bierman
Internet-Draft                                                 YumaWorks
Intended status: Standards Track                            July 3, 2017
Expires: January 4, 2018

                          YANG Data Extensions
                 draft-bierman-netmod-yang-data-ext-00

Abstract

   This document describes YANG mechanisms for extending the utility of
   the 'yang-data' extension statement defined in RFC 8040.

Status of This Memo

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   This Internet-Draft will expire on January 4, 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
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   described in the Simplified BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   2
       1.1.1.  NETCONF . . . . . . . . . . . . . . . . . . . . . . .   2
       1.1.2.  YANG  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Definitions . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Restrictions on Conceptual YANG Data  . . . . . . . . . .   3
     2.2.  YANG Data Extensions Module . . . . . . . . . . . . . . .   3
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
     3.1.  YANG Module Registry  . . . . . . . . . . . . . . . . . .   6
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   5.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   7

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
   data or state data.  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].  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, which cannot be used because a YANG compiler or
   other tool is not required to understand the "yang-data" extension.

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].

1.1.1.  NETCONF

   The following terms are defined in [RFC6241]:

   o  configuration data

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   o  state data

1.1.2.  YANG

   The following terms are defined in [RFC7950]:

   o  absolute-schema-nodeid

   o  container

   o  data node

   o  leaf

   o  leaf-list

   o  list

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 "augment-yang-data" extension.
   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-def statements or other
   "yang-data" or "augment-yang-data" statements.

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 RESTCONF
   "yang-data" extension.

   Note that there is no YANG tree diagram provided because pyang does
   not produce any tree output for a module containing only an extension
   statement.

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   <CODE BEGINS> file "yang-data-ext@2017-07-03.yang"

  module yang-data-ext {
    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>

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

    description
      "This module contains conceptual YANG specifications
       for augmenting 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 2017-07-03 {
      description
        "Initial revision.";
      reference
        "RFC XXXX: YANG Data Extensions.";
    }

    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

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         '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.

         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.

         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
         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.

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           - 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>

3.  IANA Considerations

3.1.  YANG Module Registry

   TBD

4.  Security Considerations

   This document defines a YANG extension which is used to define
   conceptual YANG data.  It does not introduce any new vulnerabilities
   beyond those specified in YANG 1.1 [RFC7950].

5.  Normative References

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

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   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, June 2011.

   [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>.

Author's Address

   Andy Bierman
   YumaWorks

   Email: andy@yumaworks.com

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