RFC7952

Internet Engineering Task Force (IETF) L. Lhotka Request for Comments: 7952 CZ.NIC Updates: 6110 August 2016 Category: Standards Track ISSN: 2070-1721

             Defining and Using Metadata with YANG

Abstract

This document defines a YANG extension that allows for defining metadata annotations in YANG modules. The document also specifies XML and JSON encoding of annotations and other rules for annotating instances of YANG data nodes.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841.

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc7952.

Copyright Notice

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.

   5.2.2.  Adding Annotations to anydata, container, and list

   5.2.3.  Adding Annotations to anyxml and leaf Instances . . .  12

Introduction

There is a need to be able to annotate instances of YANG RFC7950 data nodes with metadata. Typical use cases are as follows:

o Complementing regular data model information with

  instance-specific metadata, comments, etc.

o Providing information about the rendering of data in user

  interfaces.

o Deactivating a subtree in a configuration datastore while keeping

  the data in place.

o Network management protocols often use metadata annotations for

  various purposes in both operation requests and responses.  For
  example, the <edit-config> operation in the Network Configuration
  Protocol (NETCONF) (see Section 7.2 of RFC6241) uses annotations
  in the form of XML attributes for identifying the location in a
  configuration datastore and the type of the operation.

However, metadata annotations could potentially lead to interoperability problems if they are used in an ad hoc fashion by different parties and/or without proper documentation. A sound metadata framework for YANG should therefore satisfy these requirements:

1. The set of annotations must be extensible in a decentralized

   manner so as to allow for defining new annotations without
   running the risk of collisions with annotations defined and used
   by others.

2. The syntax and semantics of annotations must be documented, and

   the documentation must be easily accessible.

3. Clients of network management protocols such as NETCONF RFC6241

   or RESTCONF [RESTCONF] must be able to discover all annotations
   supported by a given server and identify each of them correctly.

4. Annotations sent by a server should not break clients that don't

   support them.

This document proposes a systematic way to define metadata annotations. For this purpose, the YANG extension "annotation" is defined in the module "ietf-yang-metadata" (Section 7). Other YANG modules importing this module can use the "annotation" statement for defining one or more annotations.

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

o Each annotation is bound to a YANG module name and namespace URI.

  This makes its encoding in instance documents (both XML and JSON)
  straightforward and consistent with the encoding of YANG data node
  instances.

o Annotations defined in IETF Standards Track documents are

  indirectly registered through IANA in the "YANG Module Names"
  registry RFC6020.

o Annotations are included in the data model. YANG compilers and

  tools supporting a certain annotation can thus take them into
  account and modify their behavior accordingly.

o The semantics of an annotation are defined in the "description"

  and "reference" statements.

o An annotation can be declared as conditional by using the

  "if-feature" statement.

o The type of each annotation is explicitly specified; any YANG

  built-in or derived type that is available for leaf or leaf-list
  data nodes may be specified for annotations as well.

In the XML encoding, XML attributes are a natural instrument for attaching annotations to data node instances. This document deliberately adopts some restrictions in order to remain compatible with the XML encoding of YANG data node instances and limitations of XML attributes. Specifically,

o annotations can only be scalar values.

o annotations cannot be attached to a whole list or leaf-list

  instance, only to individual list or leaf-list entries.

Due to the rules for YANG extensions (see Section 6.3.1 in RFC7950), annotation definitions posit relatively weak conformance requirements. The alternative of introducing a new built-in YANG statement for defining 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 metadata annotations, it is conceivable that such a new built-in statement might be added in a future revision of YANG.

Terminology

Key Words

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.

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 RFC7950:

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

o leaf-list

o list

o module

o Remote Procedure Call (RPC) input and output

The following terms are defined in [XML-INFOSET]:

o attribute

o document

o element

The following terms are defined in [XML-NAMES]:

o local name

o namespace name

o prefix

o qualified name

The following terms are defined in RFC7159:

o array

o member

o object

o primitive type

Namespaces and Prefixes

In the following text, XML element names and YANG extension statements are always written with explicit namespace prefixes that are assumed to be bound to URI references as shown in Table 1.

    +--------+------------------------------------------------+
    | Prefix | URI Reference                                  |
    +--------+------------------------------------------------+
    | elm    | http://example.org/example-last-modified       |
    | md     | urn:ietf:params:xml:ns:yang:ietf-yang-metadata |
    | rng    | http://relaxng.org/ns/structure/1.0            |
    +--------+------------------------------------------------+

 Table 1: Used Namespace Prefixes and Corresponding URI References

Definitions of New Terms

o annotation: a single item of metadata that is attached to YANG

  data node instances.

o metadata: additional information that complements a data tree.

o metadata object: an object in JSON encoding that contains all

  annotations attached to a given data node instance.

Defining Annotations in YANG

Metadata annotations are defined by the YANG extension "md:annotation". This YANG language extension is defined in the module "ietf-yang-metadata" (Section 7).

Substatements of "md: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 RFC7950 where each statement is described.

       +--------------+---------------------+-------------+
       | substatement | section in RFC 7950 | 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        |
       | type         | 7.6.3               | 1           |
       | units        | 7.3.3               | 0..1        |
       +--------------+---------------------+-------------+

             Table 2: Substatements of "md:annotation"

An annotation carries a single value. The "type" substatement, which MUST be present, takes as an argument the name of an existing built-in or derived type, and the value of the annotation MUST match this type. See Section 7.4 of RFC7950 for details.

An annotation can be made conditional by using one or more "if-feature" statements; the annotation is then supported only by servers that advertise the corresponding feature.

The semantics and usage rules for an annotation SHOULD be fully specified in "description", "reference", and "units" statements.

An annotation MUST NOT change the data tree semantics defined by YANG. For example, it is illegal to define and use an annotation that allows for overriding uniqueness of leaf-list entries.

The "status" statement can be used exactly as it is used for YANG data nodes.

A YANG module containing one or more "md:annotation" statements SHOULD NOT be used for defining data nodes or groupings. Also, derived types, identities, and features SHOULD NOT be defined in such a module unless they are used by the definitions of annotations in that module.

Example Definition

The following module defines the "last-modified" annotation:

module example-last-modified {

 namespace "http://example.org/example-last-modified";
 prefix "elm";
 import ietf-yang-types {
   prefix "yang";
 }
 import ietf-yang-metadata {
   prefix "md";
 }
 md:annotation last-modified {
   type yang:date-and-time;
   description
     "This annotation contains the date and time when the
      annotated instance was last modified (or created).";
 }

}

Using Annotations

By advertising a YANG module in which a metadata annotation is defined using the "md:annotation" statement, a server indicates that it is prepared to handle that annotation according to the annotation's definition. That is, an annotation advertised by the server may be attached to an instance of a data node defined in any YANG module that is implemented by the server.

Depending on its semantics, an annotation may have an effect only in certain data trees and/or on instances of specific types of data nodes.

A client MUST NOT add a specific annotation to data node instances if the server didn't advertise it.

Due care has to be exercised when introducing annotations in network management systems in order to avoid interoperability problems and software failures caused by a client that does not understand the annotations' semantics. Generally, it is safe for a server to use annotations in the following cases:

o An annotation is an integral part of a built-in or negotiated

  protocol capability.

o An annotation contains auxiliary information that is not critical

  for protocol operation.

o The client explicitly asks the server, e.g., via a parameter of a

  protocol operation request, to include an annotation in the
  response.

The Encoding of Annotations

XML attributes are a natural choice for encoding metadata in XML instance documents. For JSON RFC7159, there is no generally established method for encoding metadata. This document thus introduces a special encoding method that is consistent with the JSON encoding of YANG data node instances as defined in RFC7951.

XML Encoding

Metadata annotations are added to XML-encoded instances of YANG data nodes as XML attributes according to these rules:

o The local name of the attribute SHALL be the same as the name of

  the annotation specified in the argument of the corresponding
  "md:annotation" statement.

o The namespace of the attribute SHALL be identified by the URI that

  appears as the argument of the "namespace" statement in the YANG
  module where the annotation is defined.  It is RECOMMENDED that
  the prefix specified by the "prefix" statement in the same module
  be used in the qualified name of the attribute.

o The attribute value SHALL be encoded in the same way as the value

  of a YANG leaf instance having the same type; see Section 9 of
  RFC7950.

For example, the "last-modified" annotation defined in Section 3.1 may be encoded as follows:

<foo xmlns:elm="http://example.org/example-last-modified"

    elm:last-modified="2015-09-16T10:27:35+02:00">
 ...

</foo>

JSON Encoding

The JSON metadata encoding defined in this section has the following properties:

1. The encoding of YANG data node instances as defined in RFC7951

   does not change.

2. Namespaces of metadata annotations are encoded in the same way as

   namespaces of YANG data node instances; see RFC7951.

Metadata Object and Annotations

All metadata annotations assigned to a YANG data node instance are encoded as members (name/value pairs) of a single JSON object, henceforth denoted as the metadata object. The placement and name of this object depend on the type of the data node as specified in the following subsections.

The name of a metadata annotation (as a member of the metadata object) has the following ABNF syntax RFC5234, where the production for "identifier" is defined in Section 14 of RFC7950:

annotation-name = identifier ":" identifier

where the left identifier is the name of the YANG module in which the annotation is defined and the identifier on the right is the name of the annotation specified in the argument of the corresponding "md:annotation" statement.

Note that unlike member names of YANG data node instances in JSON encoding (see Section 4 in RFC7951), for annotations the explicit namespace identifier (module name) must always be present.

The value of a metadata annotation SHALL be encoded in exactly the same way as the value of a YANG leaf node having the same type as the annotation; see Section 6 of RFC7951.

Adding Annotations to anydata, container, and list Entries

For a data node instance that is encoded as a JSON object (i.e., a container, list entry, or anydata node), the metadata object is added as a new member of that object with the name "@".

Examples:

o "cask" is a container or anydata node:

"cask": {

 "@": {
   "example-last-modified:last-modified":
     "2015-09-16T10:27:35+02:00"
 },
 ...

}

o "seq" is a list whose key is "name"; annotation "last-modified" is

  added only to the first entry:

"seq": [

 {
   "@": {
     "example-last-modified:last-modified":
         "2015-09-16T10:27:35+02:00"
   },
   "name": "one",
   ...
 },
 {
   "name": "two",
   ...
 }

]

Adding Annotations to anyxml and leaf Instances

For an anyxml or leaf instance, the metadata object is added as a sibling name/value pair whose name is the symbol "@" concatenated with the name of the leaf or anyxml member that is being annotated. The namespace part (module name) is included if and only if it is in the name of the annotated member.

Examples:

o "flag" is a leaf node of the "boolean" type defined in module

  "foo", and we assume that the namespace name has to be expressed
  in its JSON encoding:

"foo:flag": true, "@foo:flag": {

 "example-last-modified:last-modified":
   "2015-09-16T10:27:35+02:00"

}

o "stuff" is an anyxml node:

"stuff": [1, null, "three"], "@stuff": {

 "example-last-modified:last-modified":
   "2015-09-16T10:27:35+02:00"

}

Adding Annotations to leaf-list Entries

For a leaf-list entry, which is represented as a JSON array with values of a primitive type, annotations may be assigned to one or more entries by adding a name/array pair as a sibling of the leaf-list entry, where the name is the symbol "@" concatenated with the name of the leaf-list that is being annotated, and the value is a JSON array whose i-th element is the metadata object with annotations assigned to the i-th entry of the leaf-list entry, or null if the i-th entry has no annotations.

Trailing null values in that array, i.e., those following the last non-null metadata object, MAY be omitted.

For example, in the following leaf-list instance with four entries, the "last-modified" annotation is added to the second and third entries in the following way:

"bibliomod:folio": [6, 3, 7, 8], "@bibliomod:folio": [

 null,
 { "example-last-modified:last-modified":
     "2015-06-18T17:01:14+02:00"
 },
 { "example-last-modified:last-modified":
     "2015-09-16T10:27:35+02:00"
 }

]

Representing Annotations in DSDL Schemas

RFC6110 defines the standard mapping of YANG data models to Document Schema Definition Languages (DSDL) [ISO.19757-1]. This section specifies the mapping for the extension statement "md:annotation" (Section 7), which enables validation of XML instance documents containing metadata annotations.

The first step of the DSDL mapping procedure, i.e., the transformation of the YANG data model to the hybrid schema (see Section 6 in RFC6110), is modified as follows:

1. If the data model contains at least one "md:annotation"

   statement, then a RELAX NG [ISO.19757-2] named pattern definition
   MUST be added as a child of the root <rng:grammar> element in the
   hybrid schema.  It is RECOMMENDED to use the name
   "__yang_metadata__" for this named pattern.

2. A reference to the named pattern described in item 1 MUST be

   included as a child of every <rng:element> pattern that
   corresponds to an anydata, container, leaf, leaf-list, or list
   data node.

3. Every metadata annotation definition in the form

   md:annotation ARGUMENT {
     ...
   }

   is mapped to the following RELAX NG [ISO.19757-2] pattern:

   <rng:optional>
     <rng:attribute name="PREFIX:ARGUMENT">
       ...
     </rng:attribute>
   </rng:optional>

   where PREFIX is the prefix bound to the namespace URI of the YANG
   module that contains the "md:annotation" statement.  The above
   pattern SHALL be inserted as a child of the named pattern
   described in item 1.

4. Substatements of "md:annotation" SHALL be mapped to children of

   the "rng:attribute" pattern exactly as described in Section 10 of
   RFC6110.

For example, the named pattern (item 1), when constructed only for the "last-modified" annotation, will have the following definition:

<rng:define name="__yang_metadata__">

 <rng:optional>
   <rng:attribute name="elm:last-modified">
     <rng:ref name="ietf-yang-types__date-and-time"/>
   </rng:attribute>
 </rng:optional>

</rng:define>

Every "rng:element" pattern that corresponds to an anydata, container, leaf, list, or leaf-list data node will then contain a reference to the above named pattern; for example:

<rng:element name="foo:bar">

 <rng:ref name="__yang_metadata__"/>
 ...

</rng:element>

Note that it is not necessary to use such a reference for "rng:element" patterns corresponding to anyxml data nodes because they already permit any XML attributes to be attached to their instances.

The second step of the DSDL mapping procedure, i.e., the transformation of the hybrid schema to RELAX NG [ISO.19757-2], Schematron [ISO.19757-3], and Document Semantics Renaming Language (DSRL) [ISO.19757-8] schemas, is unaffected by the inclusion of "md:annotation".

Metadata YANG Module

file "[email protected]"

module ietf-yang-metadata {

 namespace "urn:ietf:params:xml:ns:yang:ietf-yang-metadata";

 prefix "md";

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

 contact
   "WG Web:   <https://datatracker.ietf.org/wg/netmod/>

    WG List:  <mailto:[email protected]>

    WG Chair: Lou Berger
              <mailto:[email protected]>

    WG Chair: Kent Watsen
              <mailto:[email protected]>

    Editor:   Ladislav Lhotka
              <mailto:[email protected]>";

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

    Copyright (c) 2016 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 7952
    (http://www.rfc-editor.org/info/rfc7952); see the RFC itself
    for full legal notices.";

 revision 2016-08-05 {
   description
     "Initial revision.";
   reference
     "RFC 7952: Defining and Using Metadata with YANG";
 }

 extension annotation {
   argument name;
   description
     "This extension allows for defining metadata annotations in
      YANG modules.  The 'md:annotation' statement can appear only
      at the top level of a YANG module or submodule, i.e., it
      becomes a new alternative in the ABNF production rule for
      'body-stmts' (Section 14 in RFC 7950).

      The argument of the 'md:annotation' statement defines the name
      of the annotation.  Syntactically, it is a YANG identifier as
      defined in Section 6.2 of RFC 7950.

      An annotation defined with this 'extension' statement inherits
      the namespace and other context from the YANG module in which
      it is defined.

      The data type of the annotation value is specified in the same
      way as for a leaf data node using the 'type' statement.

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

      A server announces support for a particular annotation by
      including the module in which the annotation is defined among
      the advertised YANG modules, e.g., in a NETCONF <hello>
      message or in the YANG library (RFC 7950).  The annotation can
      then be attached to any instance of a data node defined in any
      YANG module that is advertised by the server.

      XML encoding and JSON encoding of annotations are defined in
      RFC 7952.";
 }

IANA Considerations

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:ietf:params:xml:ns:yang:ietf-yang-metadata
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: ietf-yang-metadata
Namespace: urn:ietf:params:xml:ns:yang:ietf-yang-metadata
Prefix: md
Reference: RFC 7952

Security Considerations

This document introduces a mechanism for defining metadata
annotations in YANG modules and attaching them to instances of YANG
data nodes. By itself, this mechanism represents no security threat.
Security implications of a particular annotation defined using this
mechanism MUST be duly considered and documented in the annotation's
definition.
An annotation SHOULD be subject to the same or stricter access
control rules as the data node instance to which the annotation is
attached. It is RECOMMENDED that security-sensitive or privacy-
sensitive data be modeled as regular YANG data nodes rather than
annotations.
10. References
10.1. 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>.

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>.

RFC6110 Lhotka, L., Ed., "Mapping YANG to Document Schema

          Definition Languages and Validating NETCONF Content",
          RFC 6110, DOI 10.17487/RFC6110, February 2011,
          <http://www.rfc-editor.org/info/rfc6110>.

RFC7159 Bray, T., Ed., "The JavaScript Object Notation (JSON) Data

          Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
          2014, <http://www.rfc-editor.org/info/rfc7159>.

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>.

RFC7951 Lhotka, L., "JSON Encoding of Data Modeled with YANG",

          RFC 7951, DOI 10.17487/RFC7951, August 2016,
          <http://www.rfc-editor.org/info/rfc7951>.

[XML-INFOSET]

          Cowan, J. and R. Tobin, "XML Information Set (Second
          Edition)", World Wide Web Consortium Recommendation
          REC-xml-infoset-20040204, February 2004,
          <http://www.w3.org/TR/2004/REC-xml-infoset-20040204>.

[XML-NAMES]

          Bray, T., Hollander, D., Layman, A., Tobin, R., and H.
          Thompson, "Namespaces in XML 1.0 (Third Edition)", World
          Wide Web Consortium Recommendation REC-xml-names-20091208,
          December 2009,
          <http://www.w3.org/TR/2009/REC-xml-names-20091208>.

10.2. Informative References
[ISO.19757-1]

          International Organization for Standardization,
          "Information Technology - Document Schema Definition
          Languages (DSDL) - Part 1: Overview", ISO/IEC 19757-1,
          September 2008.

[ISO.19757-2]

          International Organization for Standardization,
          "Information technology -- Document Schema Definition
          Language (DSDL) -- Part 2: Regular-grammar-based
          validation -- RELAX NG", ISO/IEC 19757-2:2008, December
          2008.

[ISO.19757-3]

          International Organization for Standardization,
          "Information technology -- Document Schema Definition
          Languages (DSDL) -- Part 3: Rule-based validation --
          Schematron", ISO/IEC 19757-3:2016, January 2016.

[ISO.19757-8]

          International Organization for Standardization,
          "Information Technology - Document Schema Definition
          Languages (DSDL) - Part 8: Document Semantics Renaming
          Language - DSRL", ISO/IEC 19757-8:2008(E), December 2008.

[RESTCONF] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF

          Protocol", Work in Progress,
          draft-ietf-netconf-restconf-16, August 2016.

RFC6241 Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,

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

Acknowledgements
The author wishes to thank Andy Bierman, Martin Bjorklund, Benoit
Claise, Juergen Schoenwaelder, and Kent Watsen for their helpful
comments and suggestions.
Author's Address
Ladislav Lhotka
CZ.NIC
Email: [email protected]

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Contents

Introduction

Terminology

Key Words

Terms Defined in Other Documents

Namespaces and Prefixes

Definitions of New Terms

Defining Annotations in YANG

Example Definition

Using Annotations

The Encoding of Annotations

XML Encoding

JSON Encoding

Metadata Object and Annotations

Adding Annotations to anydata, container, and list Entries

Adding Annotations to anyxml and leaf Instances

Adding Annotations to leaf-list Entries

Representing Annotations in DSDL Schemas

Metadata YANG Module

IANA Considerations

Security Considerations

Navigation

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RFC7952

Contents

Introduction

Terminology

Key Words

Terms Defined in Other Documents

Namespaces and Prefixes

Definitions of New Terms

Defining Annotations in YANG

Example Definition

Using Annotations

The Encoding of Annotations

XML Encoding

JSON Encoding

Metadata Object and Annotations

Adding Annotations to anydata, container, and list Entries

Adding Annotations to anyxml and leaf Instances

Adding Annotations to leaf-list Entries

Representing Annotations in DSDL Schemas

Metadata YANG Module

IANA Considerations

Security Considerations

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