Internet DRAFT - draft-vassilev-netmod-yang-direct-must-augment-ext

draft-vassilev-netmod-yang-direct-must-augment-ext






Network Working Group                                        V. Vassilev
Internet-Draft                                               Transpacket
Intended status: Standards Track                           June 12, 2015
Expires: December 14, 2015


                   YANG Direct Must Augment Extension
         draft-vassilev-netmod-yang-direct-must-augment-ext-00

Abstract

   This document introduces new YANG extension statement for assignment
   of must sub-statements to existing data nodes through augment without
   the requirement for a parent data node containing the must statement.

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
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   This Internet-Draft will expire on December 14, 2015.

Copyright Notice

   Copyright (c) 2015 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.





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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  3
       1.1.1.  YANG . . . . . . . . . . . . . . . . . . . . . . . . .  3
       1.1.2.  Tree Diagrams  . . . . . . . . . . . . . . . . . . . .  3
     1.2.  Problem Statement  . . . . . . . . . . . . . . . . . . . .  4
     1.3.  Solution . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Using Direct Must Augment Extension  . . . . . . . . . . . . .  5
   3.  Direct Must Augment Extension Module . . . . . . . . . . . . .  6
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  8
     4.1.  DIRECT-MUST-AUGMENT-EX XML Namespace . . . . . . . . . . .  8
     4.2.  DIRECT-MUST-AUGMENT-EX YANG Module . . . . . . . . . . . .  8
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   6.  Normative References . . . . . . . . . . . . . . . . . . . . . 10
   Appendix A.  Example Data Models . . . . . . . . . . . . . . . . . 11
     A.1.  Model of a Generic Entertainment Facility  . . . . . . . . 11
     A.2.  Model of a Casino  . . . . . . . . . . . . . . . . . . . . 13
     A.3.  Model of a Zoo . . . . . . . . . . . . . . . . . . . . . . 13
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 16































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1.  Introduction

   The possibility to introduce new sub-statements to existing data
   nodes available in YANG [RFC6020] provides great flexibility to the
   authors of data models.  However not all sub-statements can be added
   to existing data nodes through augment.  It is not possible to add
   new must sub-statements.  In certain use cases this limitation
   complicates the task of expressing valid data constraints as must
   statements.  This document explains the problem Section 1.2 and
   proposes a solution Section 1.3.

1.1.  Terminology

   The keywords "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].

1.1.1.  YANG

   The following terms are defined in [RFC6020]:

   o  must statement

   o  augment statement

   o  context node

   o  container

   o  data node

   o  key leaf

   o  leaf

   o  leaf-list

   o  list

1.1.2.  Tree Diagrams

   A simplified graphical representation of the data model is used in
   this document.  The meaning of the symbols in these diagrams is as
   follows:






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   o  Brackets "[" and "]" enclose list keys.

   o  Abbreviations before data node names: "rw" means configuration
      (read-write) and "ro" state data (read-only).

   o  Symbols after data node names: "?" means an optional node and "*"
      denotes a "list" and "leaf-list".

   o  Parentheses enclose choice and case nodes, and case nodes are also
      marked with a colon (":").

   o  Ellipsis ("...") stands for contents of subtrees that are not
      shown.

1.2.  Problem Statement

   This document attempts to address the problem YANG model authors
   encounter when expressing valid data constraints with must statements
   and wish to use existing model data node as context node for the
   Xpath expression.  The problem is significant in the cases where the
   context data node has to be evaluated as part of a relative path
   expressions using . or current().  An example where this problem is
   encountered is the design of entertainment facility data model.  The
   existing model defines a list of facilities.  Each with identity leaf
   and list of visitors.  The authors task is to design a model for a
   casino and a zoo.  For the casino he only needs to define the
   identity and a constraint for the visitors to be adults older then
   18.  For the zoo except the identity definition he has to define a
   constraint that allows only children with adult supervision to be
   included in the visitors list.

1.3.  Solution

   This document defines a YANG extension of the augment statement -
   ietf-direct-must-augment-extension:augment.  The extension accepts
   must as sub-statement.  The extension enables model authors to
   specify must statements with context nodes in existing models.

   The extension is completely backward-compatible with the current
   definitions in [RFC6020].  An old YANG parser will ignore any must
   statements introduced by ietf-direct-must-augment-extension:augment
   No existing models are affected by the new extension, so its
   introduction will be transparent to the existing YANG parsers.








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2.  Using Direct Must Augment Extension

   A YANG extension statement "ietf-direct-must-augment-
   extension:augment" is introduced in the YANG module in Section 3.
   Its intended use is to allow must as sub-statement which is not
   possible with the augment statement defined in [RFC6020].  For
   example:


   module entertainment-facilities-casino {
   ...
     identity casino {
       base ef:entertainment-facility-generic;
     }

     direct-must-augment-ex:augment
       "/ef:entertainment-facilities/ef:entertainment-facility" +
       "ef:visitor" {
       when "../ef:type='ef-casino:casino'";
       must "(/people/person[name=current()]/age>=18)" {
         error-message
           "Only adults are allowed in a casino.";
       }
     }
   }


























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3.  Direct Must Augment Extension Module

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

   <CODE BEGINS> file
   "ietf-direct-must-augment-extension@2015-06-12.yang"

  module ietf-direct-must-augment-extension {

    namespace
      "urn:ietf:params:xml:ns:yang:ietf-direct-must-augment-extension";
    prefix "direct-must-augment-ex";

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

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

       Editor:   Vladimir Vassilev
                 <mailto:vladimir@transpacket.com>";

    description
      "This module contains extension of the standard augment statement.

       Copyright (c) 2015 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).

       This version of this YANG module is part of RFC XXXX; see
       the RFC itself for full legal notices.";

    // RFC Ed.: replace XXXX with actual RFC number and remove this
    // note.

    // RFC Ed.: update the date below with the date of RFC publication
    // and remove this note.
    revision 2015-06-12 {
      description
        "Initial revision.";



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      reference
        "RFC XXXX: Direct Must Augment Extension";
    }

    /*
     * Extension
     */

    extension augment {
      argument target;
      description
        "This extension introduces a direct must augment statement
         capable of augmenting existing data nodes with new must
         sub-statements.";
    }
  }


   <CODE ENDS>
































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4.  IANA Considerations

4.1.  DIRECT-MUST-AUGMENT-EX XML Namespace

   This document registers a URI in the IETF XML registry [RFC3688].
   Following the format in RFC 3688, the following registration is
   requested:

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

4.2.  DIRECT-MUST-AUGMENT-EX YANG Module

   This document registers 1 YANG module in the YANG Module Names
   registry [RFC6020].

 name:    ietf-direct-must-augment-extension
 namespace:
          urn:ietf:params:xml:ns:yang:ietf-direct-must-augment-extension
 prefix:  direct-must-augment-ex
 // RFC Ed. remove this line and replace XXXX in next line
 reference:    RFC XXXX




























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5.  Security Considerations

   This document does not introduce any new security concerns in
   addition to those specified in [RFC6020], section 15.















































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6.  Normative References

   [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.

   [RFC6020]  Bjorklund, M., "YANG - A Data Modeling Language for the
              Network Configuration Protocol (NETCONF)", RFC 6020,
              October 2010.

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

   [RFC6991]  Schoenwaelder, J., "Common YANG Data Types", RFC 6991,
              July 2013.

   [XSD]      Malhotra, A. and P. Biron, "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>.




























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Appendix A.  Example Data Models

A.1.  Model of a Generic Entertainment Facility

   The "entertainment-facilities" YANG module models a collection of
   people and entertainment-facilities.  Each person in the people
   collection has a name and age.  Each entertainment-facility has a
   name, type and list of visitors referencing entries in the people
   collection.  This example model is the target module for direct must
   augment extension statements defined in Appendix A.2 and
   Appendix A.3.

   module: entertainment-facilities
      +--rw people
      |  +--rw person* [name]
      |     +--rw name    string
      |     +--rw age     uint32
      +--rw entertainment-facilities
         +--rw entertainment-facility* [name]
            +--rw name       string
            +--rw type       identityref
            +--rw visitor*   -> /people/person/name



   module entertainment-facilities {
     namespace "http://example.com/ns/entertainment-facilities";
     prefix entertainment-facilities;
     organization "Example, Inc.";
     contact "support@example.com";

     description
       "Module used in DIRECT-MUST-AUGMENT-EX example.";

     revision 2015-06-12 {
       description "Initial version";
     }

     container people {
       description
         "Contains all people.";

       list person {
         key name;

         leaf name {
           type string;
         }



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         leaf age {
           type uint32;
           mandatory true;
         }
       }
     }

     identity entertainment-facility-generic {
       description
         "Base identity from which specific" +
         "entertainment facility types are derived.";
     }

     container entertainment-facilities {
       description
         "Container for all entertainment-facilities information.";

       list entertainment-facility {
         key name;

         leaf name {
           type string;
         }

         leaf type {
           type identityref {
             base entertainment-facility-generic;
           }
           mandatory true;
         }

         leaf-list visitor {
           type leafref {
             path "/people/person/name";
           }
         }
       }
     }
   }












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A.2.  Model of a Casino

   module entertainment-facilities-casino {
     namespace "http://example.com/ns/entertainment-facilities-casino";
     prefix ef-casino;
     import ietf-direct-must-augment-extension
       { prefix direct-must-augment-ex; }
     import entertainment-facilities { prefix ef; }
     organization "Example, Inc.";
     contact "support@example.com";

     description
       "Module used in DIRECT-MUST-AUGMENT-EX example. " +
       "Defines entertainment facility of type casino where" +
       "only adults are allowed.";

     revision 2015-06-12 {
       description "Initial version";
     }

     identity casino {
       base ef:entertainment-facility-generic;
     }

     direct-must-augment-ex:augment
       "/ef:entertainment-facilities/ef:entertainment-facility/" +
       "ef:visitor" {
       when "../ef:type='ef-casino:casino'";
       must "(/people/person[name=current()]/age>=18)" {
         error-message
           "Only adults are allowed in a casino.";
       }
     }
   }

A.3.  Model of a Zoo

   module: entertainment-facilities-zoo
   augment /ef:entertainment-facilities/ef:entertainment-facility:
      +--rw child-supervision* [child]
         +--rw child    -> ../../ef:visitor
         +--rw adult    -> ../../ef:visitor


 module entertainment-facilities-zoo {
   namespace "http://example.com/ns/entertainment-facilities-zoo";
   prefix ef-zoo;
   import ietf-direct-must-augment-extension



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     { prefix direct-must-augment-ex; }
   import entertainment-facilities { prefix ef; }
   organization "Example, Inc.";
   contact "support@example.com";

   description
     "Module used in DIRECT-MUST-AUGMENT-EX example. " +
     "Defines entertainment facility of type zoo where" +
     "no children without adult supervision are allowed.";

   revision 2015-06-12 {
     description "Initial version";
   }

   identity zoo {
     base ef:entertainment-facility-generic;
   }
   augment
     "/ef:entertainment-facilities/ef:entertainment-facility" {
     when "ef:type='ef-zoo:zoo'";
     list child-supervision {
       key child;
       leaf child {
         type leafref {
           path "../../ef:visitor";
         }
         must "/people/person[name=current()]/age<=14" {
           error-message
             "People older then 14 are not children.";
         }
       }
       leaf adult {
         mandatory true;
         type leafref {
           path "../../ef:visitor";
         }
         must "/people/person[name=current()]/age>=18" {
           error-message
             "People younger then 18 are not adults.";
         }
       }
     }
   }

   direct-must-augment-ex:augment
     "/ef:entertainment-facilities/ef:entertainment-facility/" +
     "ef:visitor" {
     when "../ef:type='ef-zoo:zoo'";



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     must "((../child-supervision[child=current()]) or
           (/people/person[name=current()]/age>=14))" {
       error-message
         "Children without adult supervision are not allowed in a zoo.";
     }
   }
 }












































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Author's Address

   Vladimir Vassilev
   Transpacket

   Email: vladimir@transpacket.com













































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