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Versions: 00 01

Internet Draft                                             Vinod Kumar S
NETMOD Working Group                                      Gaurav Agrawal
Category: Operational                                     Anil Kumar S N
Expires: December 30, 2016                           Huawei Technologies
                                                           June 28, 2016


             Defining and Using Metadata for YANG compilers
               draft-agv-netmod-yang-compiler-metadata-00

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on December 30, 2016.

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   This document is subject to BCP 78 and the IETF Trust's Legal
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Abstract

   This document defines a YANG extension statement that allows for
   defining compiler metadata (annotations) in YANG modules.



Table of Contents

   1. Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
     2.1.  Keywords . . . . . . . . . . . . . . . . . . . . . . . . .  5
     2.2.  Terms Defined in Other Documents . . . . . . . . . . . . .  5
     2.4.  Definitions of New Terms . . . . . . . . . . . . . . . . .  6
   3.  Defining compiler annotations in YANG  . . . . . . . . . . . .  6
     3.1.  Example Definition . . . . . . . . . . . . . . . . . . . .  8
   4.  Using Annotations  . . . . . . . . . . . . . . . . . . . . . .  9
   5.  Metadata YANG Module . . . . . . . . . . . . . . . . . . . . .  9
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13
   9 Security Considerations  . . . . . . . . . . . . . . . . . . . . 13
   10.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
   11 References  . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     11.1 Normative References  . . . . . . . . . . . . . . . . . . . 14
     11.2 Informative References  . . . . . . . . . . . . . . . . . . 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15


























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1. Introduction

   YANG started as a data modeling language used to model configuration
   data, state data, remote procedure calls, and notifications for
   network  management protocols. The purpose of YANG was focused on
   expressing the data organization while being exchanged over network.
   It also addressed the constraints that needs to be taken care by the
   data set exchanged.

   YANG has out grown the purpose for which it was invented. Due to its
   simplicity in structure and flexibility many tools have been
   developed which tries to ease the application development by
   automating the code generated corresponding to defined schema.

   All the implementation related data structures / classes could be
   auto generated and applications only concentrate on the business
   logic implementation. Applications are being relieved from actual
   protocol implementation for exchanging information with external
   system.

   The purpose of YANG was focused on expressing the data organization
   while being exchanged over network. Hence the scope of automation in
   application development cannot cater to data organization /
   processing within the system.

   So there is a need to support compiler annotations in YANG, by which
   applications can instruct the YANG utilities or compilers to automate
   the application development related to data organization /
   processing. Typical use cases are:

   o  Feed input to YANG compiler/utilities which can be used to
      automate the code generation based on standard data structure or
      collections.

   o  Enable the code generation to incorporate the design patterns
      required by applications.

   o  Enable the data structure or collections to have multiple indexes
      beyond the current supported list's key(s). Since the actual
      implementation would required searching the data based on
      different leaf combinations.

   o  Enable applications to model internal data organization, required
      for business logic implementation, and not exposed to outside
      world.

   Usage of compiler annotations are dependent on the compiler consuming
   it. This draft is intended to document YANG extension to support



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   defining compiler annotation framework.It is outside the scope of
   this document about the specific compiler annotation(s) definition /
   usage. Individual annotation definition and usage SHOULD be
   standardized in other docs.

   Definition and usage of compiler annotation is limited to a
   particular protocol or application development within a device, it
   has no effect on how the management information is exchanged between
   2 devices over network. A server SHOULD share its YANG file(s) after
   removing the compiler annotations that was added for its
   implementation. A client MUST ignore any compiler annotations present
   in the YANG file(s). A client MAY redefine the compiler annotation as
   per its implementation requirements. Clients MAY also add new
   annotation depending on its implementation requirements.

   This document proposes a systematic way for defining compiler
   metadata annotations.  For this purpose, YANG extension statement
   "compiler-annotation" is defined in the module "agv-yang-compiler-
   annotation" (Section 5).  Other YANG modules importing this module
   can use the "compiler-annotation" statement for defining one or more
   compiler annotations.

   The benefits of defining the compiler-annotations in a YANG module
   are the following:

   o  Applications can use YANG as a tool to design the application
      implementation.

   o  Enhance the YANG compiler(s) capability to automate the
      application development process.

   o  Enhance the protocol development to provide better application
      development framework.

   o  YANG could be extended to support data modeling for protocol
      beyond NETCONF or RESTCONF.

   Due to the rules for YANG extensions (see sec. 6.3.1 in [I-D.ietf-
   netmod-rfc6020bis]), compiler-annotation definitions posit relatively
   weak conformance requirements.  The alternative of introducing a new
   built-in YANG mechanism for compiler annotations was considered, but
   it was seen as a major change to the language that is inappropriate
   for YANG 1.1, which was chartered as a maintenance revision.  After
   evaluating real-life usage of compiler metadata annotations, it is
   designed in such way that the ABNF grammar can seamlessly adapt the
   current defined compiler annotations.





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2.  Terminology

2.1.  Keywords

   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].

2.2.  Terms Defined in Other Documents

      The following terms are defined in [RFC6241]:

         o  capability,

         o  client,

         o  datastore,

         o  message,

         o  protocol operation,

         o  server.

      The following terms are defined in [I-D.ietf-netmod-rfc6020bis]:

         o  action,

         o  anydata,

         o  anyxml,

         o  built-in type,

         o  container,

         o  data model,

         o  data node,

         o  data tree,

         o  derived type,

         o  extension,

         o  leaf,




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         o  leaf-list,

         o  list,

         o  module,

         o  RPC input and output.

2.4.  Definitions of New Terms

      o  compiler-annotation: a single item of compiler metadata that is
         attached to YANG constructs.
      o  compiler metadata: additional information that complements a
         schema tree.
      o  metadata object: an object in JSON encoding that contains all
         annotations attached to a given data node instance.

3.  Defining compiler annotations in YANG

   Compiler metadata annotations are defined by YANG extension statement
   "ca:compiler-annotation".  This YANG language extension is defined in
   the module "agv-yang-compiler-annotation" (Section 5).

   sub-statements of "ca:compiler-annotation" are shown in Table 2.
   They are all core YANG statements, and the numbers in the second
   column refer to the corresponding section in [I-D.ietf-netmod-
   rfc6020bis] where each statement is described.

          +---------------+---------------------+-------------+
          | sub-statement | RFC 6020bis section | cardinality |
          +---------------+---------------------+-------------+
          |  description  | 7.21.3              | 0..1        |
          |  if-feature   | 7.20.2              | 0..n        |
          |  reference    | 7.21.4              | 0..1        |
          |  status       | 7.21.2              | 0..1        |
          |  units        | 7.3.3               | 0..1        |
          |  @ANNOTATION  | Current Section 5   | 1..n        |
          +---------------+---------------------+-------------+

           Table 2: Substatements of "ca:compiler-annotation".

   A YANG construct can have one or more compiler annotation.  The
   @ANNOTATION substatement, which MUST be present at least once,
   follows the ABNF specification as defined in section 5.

   An compiler annotation can be made conditional by using one or more
   "if- feature" statements; the compiler annotation is then consumed by
   compilers and perform the desired operation in compilation.



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   The semantics and usage rules for a compiler-annotation SHOULD be
   fully specified in another document.

   A compiler-annotation MUST NOT change the schema tree semantics
   defined by YANG.  For example, it is illegal to define and use an
   compiler-annotation that allows modification to data-def-stmts.

   The "status" statement can be used exactly as for YANG schema nodes.











































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3.1.  Example Definition

   The following module defines the "MappedCollection" compiler-
   annotation:

     module example-compiler-annotation {

     namespace "urn:agv:params:xml:ns:yang:example-compiler-annotation";

     prefix "example";

     import agv-yang-compiler-annotation{
       prefix "ca";
     }

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

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

     description
       "This YANG module demonstrates the usage of compiler annotation
       by any module.";

     revision 2016-06-22 {
       description
         "Initial revision.";
       reference
         "RFC draft agv: example of defining and using compiler
          annotations with YANG";
     }

     container candidate-servers{
       list server {
         ca:compiler-annotation{
           @MappedCollection(collection-type='map', map-key='name')
           @OverrideImpl('DefaultServer');
         }

         key "name";
         unique "ip port";
         leaf name {
           type string;
         }
         leaf ip {
           type inet:ip-address;



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         }
         leaf port {
           type inet:port-number;
         }
       }
     }
    }

4.  Using Annotations

   By defining a YANG module in which a compiler metadata annotation is
   defined using the "ca:compiler-annotation" statement, an application
   indicates compiler to handle that compiler-annotation according to
   the compiler-annotation's definition.  That is, the compiler-
   annotation uses it as input for automation of code generation or
   applications development.

   Depending on its semantics, an annotation may have an effect only in
   certain schema trees and/or on specific schema node types.

   A client MUST NOT use the compiler-annotation to interpret the schema
   even if it is advertised by a server.

5.  Metadata YANG Module

   RFC Editor: In this section, replace all occurrences of 'XXXX' with
   the actual RFC number and all occurrences of the revision date below
   with the date of RFC publication (and remove this note).

   RFC Editor: Also please replace all occurrences of 'RFC 6020bis' with
   the actual RFC number that will be assigned to [I-D.ietf-netmod-
   rfc6020bis].



















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   <CODE BEGINS> file "agv-yang-compiler-annotation.yang"

   module agv-yang-compiler-annotation {

   namespace "urn:agv:params:xml:ns:yang:agv-yang-compiler-annotation";

   prefix "ca";

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

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

   description
     "This YANG module defines an extension statement that allows for
      defining compiler annotations.

      The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL
      NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'MAY', and
      'OPTIONAL' in the module text are to be interpreted as described
      in RFC 2119 (http://tools.ietf.org/html/rfc2119).";

     revision 2016-06-22 {
     description
       "Initial revision.";
     reference
       "RFC draft agv: Defining and Using compiler annotations with
       YANG";
     }

     extension compiler-annotation {
     description
       "This extension allows for defining compiler annotations for
        any body-stmts. The 'ca:compiler-annotation' statement
        contains annotations applicable to its parent statement.

        It's purpose is to provide additional information to compiler
        about internal implementation of the modeled information.

        It MAY be consumed by the compiler of the device supporting
        the schema.

        The peer device using the schema for communication, MUST NOT
        depend on the ca:compiler-annotations for interpreting the
        schema of the information exchanged.




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        The ca:compiler-annotation defined with this extension
        statement do not affect the namespace or get impacted by
        the namespace of the YANG file where it is used.

        Semantics of the annotation and other documentation can be
        specified using the following standard YANG substatements (all
        are optional):  'description', 'reference', 'status', and
        'units'.

        The presence of a 'if-feature' child to the ca:
        compiler-annotation, means the compiler consumes the
        annotation when the feature is supported by the device.

        Server MAY trim the ca:compiler-annotations in the schema
        while sharing it to a client in protocol exchange.

        Client receiving the schema from a Server in protocol
        exchange, SHOULD ignore the ca:compiler-annotations present
        in the schema definition.

        The must be 1 or more child entries with '@ANNOTATION_NAME'
        as per the compiler-annotation ABNF grammar defined in draft
        agv-yang-compiler-annotation.

        compiler-annotation-stmt = compiler-annotation-keyword optsep
                     \"{\" stmtsep
                         ;; these stmts can appear in any order
                          [description-stmt stmtsep]
                         *(if-feature-stmt stmtsep)
                          [reference-stmt stmtsep]
                          [status-stmt stmtsep]
                          [units-stmt stmtsep]
                          1*(annotation-stmt stmtsep)
                     \"}\"

        annotation-stmt = \"@\" annotation-type
                              [annotation-parameter-specification] \";\"

        annotation-type = identifier

        annotation-parameter-specification =
       \"(\" optsep annotation-parameter-specification-arg optsep \")\"

       annotation-parameter-specification-arg = annotation-para-value /
              annotation-para-instance *(\",\" annotation-para-instance)

        annotation-para-instance = annotation-para-type-identifier
                               optsep \"=\" optsep annotation-para-value



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        annotation-para-type-identifier = identifier
        annotation-para-value = identifier


        The choosen ABNF can be updated in YANG 2.0 as part of any
        body-stmts and this extension can be obsloted";
      } // compiler-annotation
   } //module agv-yang-compiler-annotation

   <CODE ENDS>









































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8.  IANA Considerations

      RFC Editor: In this section, replace all occurrences of 'XXXX'
   with   the actual RFC number and all occurrences of the revision date
   below   with the date of RFC publication (and remove this note).

      This document registers a URI in the "IETF XML registry"
   [RFC3688].   Following the format in RFC 3688, the following
   registration has been   made.

      ------------------------------------------------------------------
      URI: urn:agv:params:xml:ns:yang:agv-yang-compiler-annotation

      Registrant Contact: The NETMOD WG of the IETF.

      XML: N/A, the requested URI is an XML namespace.
      ------------------------------------------------------------------

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

      ------------------------------------------------------------------
      name:         agv-yang-compiler-annotation
      namespace:    urn:agv:params:xml:ns:yang:
                                            agv-yang-compiler-annotation
      prefix:       md
      reference:    RFC XXXX
      ------------------------------------------------------------------

9 Security Considerations

   This document introduces a mechanism for defining compiler metadata
   annotations in YANG modules and attaching them to instances of YANG
   schema nodes.  By itself, this mechanism represents no security
   threat. Security implications of a particular compiler-annotation
   defined using this mechanism MUST be duly considered and documented
   in the the compiler-annotation's definition.

10.  Acknowledgments












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11 References

11.1 Normative References

      I-D.ietf-netmod-rfc6020bis]
                Bjorklund, M., "The YANG 1.1 Data Modeling Language",
                draft-ietf-netmod-rfc6020bis-11 (work in progress),
                February 2016.

      I-D.ietf-netmod-yang-json]
                Lhotka, L., "JSON Encoding of Data Modeled with YANG",
                draft-ietf-netmod-yang-json-09 (work in progress), March
                2016.

      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>.

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

      RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for
                Syntax Specifications: ABNF", STD 68, RFC 5234,
                DOI 10.17487/RFC5234, January 2008,
                <http://www.rfc-editor.org/info/rfc5234>.

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

11.2 Informative References

      [I-D.ietf-netconf-restconf]
                 Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
                 Protocol", draft-ietf-netconf-restconf-10 (work in
                 progress), March 2016.

      [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J.,
                 and A. Bierman, Ed., "Network Configuration Protocol
                 (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
                 <http://www.rfc-editor.org/info/rfc6241>.







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Authors' Addresses


      Vinod Kumar S
      Huawei Technologies India Pvt. Ltd,
      Near EPIP Industrial Area,
      Kundalahalli Village,
      Whitefield,
      Bangalore - 560066

      EMail: vinods.kumar@huawei.com

      Gaurav Agrawal
      Huawei Technologies India Pvt. Ltd,
      Near EPIP Industrial Area,
      Kundalahalli Village,
      Whitefield,
      Bangalore - 560066

      EMail: gaurav.agrawal@huawei.com

      Anil Kumar S N
      Huawei Technologies India Pvt. Ltd,
      Near EPIP Industrial Area,
      Kundalahalli Village,
      Whitefield,
      Bangalore - 560066

      EMail: anil.ietf@gmail.com






















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