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NETCONF Data Modeling Language                                  L. Bertz
Internet-Draft                                                    Sprint
Intended status: Standards Track                           March 9, 2017
Expires: September 10, 2017


                YANG extension for Common Augmentations
                  draft-bertz-netmod-commonaugment-01

Abstract

   This document defines a YANG extension to convey common schema
   augmentations.

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 September 10, 2017.

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

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November



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   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

1.  Introduction

   This document provides a mechanism for the specification of an
   augmentation at multiple locations of a YANG schema using the
   extension statement as defined in Section 7.15 of [RFC7950].

   YANG extensions commonly add one augmentation to a common structure.
   Figure 1 shows a small module and another that will be used to extend
   it.
































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                              ... basemodule {
                                prefix b;
                                ...
                                grouping base_element {
                                    ...
                                }

                                rpc my_rpc {
                                  input {
                                    uses b:base_element;
                                  }
                                  output {
                                    uses b:base_element;
                                  }
                                }

                                rpc my_bestrpc {
                                  input {
                                    uses b:base_element;
                                  }
                                }
                              }

                              ... newstuffmodule {
                                grouping new_things {
                                  ...
                                }
                              }


                        Figure 1: Reference Modules

   When extending my_rpc in the base module by adding new_things to the
   base element, one must use two augment statements.  If the author of
   the newstuff module wishes to extend base_element then they must
   write an augment statement for every schema location it which it
   appears.

   An extension with the key word "also-augments" is proposed that
   allows one augment statement to be used for augmentations.

   Figure 2 shows the traditional and common augment examples.









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     module old_way {
       import base { prefix base_module; }
       import newstuff { prefix new_module; }
       augment "/base_module:my_rpc/base_element/input" {
         uses new_module:new_things;
       }
       augment "/base_module:my_rpc/base_element/output" {
         uses new_module:new_things;
       }
       augment "/base_module:my_bestrpc/base_element/input" {
         uses new_module:new_things;
       }
     }

     module new_way {
        import base { prefix base_module; }
        import newstuff { prefix new_module; }
        import commonaugment { prefix c; }

        augment "/base_module:my_rpc/base_element/input" {
          uses new_module:new_things;

          c:also-augments "/base_module:my_rpc/base_element/output";
          c:also-augments "/base_module:my_bestrpc/base_element/input";
        }
      }


                         Figure 2: Augment Options

   The also-augments statement takes a single argument that is the same
   one defined for the augment statement [RFC7950].

   This has two purposes:

      Reduces the amount of YANG written when common augmentations are
      invovled.

      Provides a hint to the tools that translate YANG to code that a
      common augmentation exists.

   The importance of the second benefit for is significant as it permits
   them to leverage any common structure or inheritence functions.








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2.  Requirements Language

   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 RFC 2119 [RFC2119].

3.  Overview

   This module defines only the also-augmennts extension.  This
   extension is ONLY meaningful as a child of an augment statement and
   is otherwise ignored.  It is semantically equivalent to writing an
   augment statement whose target node is the argument of the also-
   augment node.  This is shown in Figure 3.

        augment "/base_module:my_rpc/base_element/input" {
          uses new_module:new_things;
        }
        augment "/base_module:my_rpc/base_element/output" {
          uses new_module:new_things;
        }

        ... semantically equivalent version below ...

        augment "/base_module:my_rpc/base_element/input" {
          uses new_module:new_things;

          c:also-augments "/base_module:my_rpc/base_element/output";
        }

             Figure 3: Statement Equivalence of also-augments

   Multiple also-augments statements MAY appear in a single augment
   statement.

   This statement MAY appear in a module that is intended to be
   backwards compatible as shown in Figure 4.  In such cases, it is used
   as a hint to readers and compilation software that the augmentations
   are intended to be the same augmentation at multiple schema tree
   locations.












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        augment "/base_module:my_rpc/base_element/input" {
          uses new_module:new_things;
          c:also-augments "/base_module:my_rpc/base_element/output";
        }
        augment "/base_module:my_rpc/base_element/output" {
          uses new_module:new_things;
        }

           Figure 4: Backwards compatible usage of also-augment

4.  Module Definition

   This section contains the module definition.

   <CODE BEGINS> file "ietf-commonaugment@2017-03-04.yang"
   module ietf-commonaugment {
       yang-version 1.1;
       namespace "urn:ietf:params:xml:ns:yang:ietf-commonaugment";
       prefix commonaug;

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

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

           WG Chair: Lou Berger
                     <mailto:lberger@labn.net>

           WG Chair: Kent Watsen
                     <mailto:kwatsen@juniper.net>

           Editor:   Lyle Bertz
                     <mailto:lyleb551144@gmail.com>";

       description
       "This module contains YANG definition for
        common augments.

        Copyright (c) 2016 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



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        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.";

       revision 2017-03-04 {
           description "Initial Revision.";
           reference "draft-bertz-netmod-commonaugment-00";
       }

       extension also-augments {
         argument "target-node";
         description
           "The argument is a string that identifies a node in the
           schema tree and is the same argument that is defined for
           the YANG argument statement";
       }
   }
   <CODE ENDS>

5.  IANA Considerations

   This document registers six URIs in the "IETF XML Registry"
   [RFC3688].  Following the format in RFC 3688, the following
   registrations have been made.

      URI: urn:ietf:params:xml:ns:yang:commonaug
      Registrant Contact: The NETMOD WG of the IETF.
      XML: N/A, the requested URI is an XML namespace.

   This document registers the following YANG module in the "YANG Module
   Names" registry [RFC7950].

           name:         ietf-dmm-fpc
           namespace:    urn:ietf:params:xml:ns:yang:commonaug
           prefix:       commonaug
           reference:    TBD1

6.  Security Considerations

   This document provides an alternative mechanism to express
   augmentations that can exist in a YANG module.  It does not provide
   new informaiton elements to the module but does provide a hint as to
   the commonality of a set of augment statements.  This, however,
   SHOULD have already been described in the module's definition or
   specification.  Thus, the use of this statement does not yield new
   information.




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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,
              <http://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,
              <http://www.rfc-editor.org/info/rfc7950>.

7.2.  Informative References

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

Author's Address

   Lyle Bertz
   Sprint
   6220 Sprint Parkway
   Overland Park, KS  66251
   United States

   Email: lylebe551144@gmail.com























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