YANG Module Tags
draft-ietf-netmod-module-tags-02

Abstract

This document provides for the association of tags with YANG modules. The expectation is for such tags to be used to help classify and organize modules. A method for defining, reading and writing a modules tags is provided. Tags may be standardized and assigned during module definition; assigned by implementations; or dynamically defined and set by users. This document provides guidance to future model writers and, as such, this document updates [I-D.ietf-netmod-rfc6087bis].

Status of This Memo

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This Internet-Draft will expire on January 2, 2019.

Copyright Notice

Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved.

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Table of Contents

• 1. Introduction
• 2. Conventions Used in This Document
• 3. Tag Prefixes
• 3.1. IETF Standard Tags
• 3.2. Vendor Tags
• 3.3. Local Tags
• 3.4. Reserved Tags
• 4. Tag Management
• 4.1. Module Definition Association
• 4.2. Implementation Association
• 4.3. Administrative Tagging
• 5. Tags Module Structure
• 5.1. Tags Module Tree
• 5.2. Tags Module
• 6. Other Classifications
• 7. Guidelines to Model Writers
• 7.1. Define Standard Tags
• 8. IANA Considerations
• 8.1. YANG Module Tag Prefix Registry
• 8.2. YANG Module IETF Tag Registry
• 9. References
• 9.1. Normative References
• 9.2. Informative References
• Authors' Addresses

1. Introduction

The use of tags for classification and organization is fairly ubiquitous not only within IETF protocols, but in the internet itself (e.g., #hashtags). Tags can be usefully standardized, but they can also serve as a non-standardized mechanism available for users to define themselves. Our solution provides for both cases allowing for the most flexibility. In particular, tags may be standardized as well as assigned during module definition; assigned by implementations; or dynamically defined and set by users.

This document defines a module which provides a list of module entries to allow for adding or removing of tags as well as viewing the set of tags associated with a module.

This document also defines an IANA registry for tag prefixes as well as a set of globally assigned tags.

Section 7 provides guidelines for authors of YANG data models. This section updates [I-D.ietf-netmod-rfc6087bis].

2. Conventions Used in This Document

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].

Note that lower case versions of these key words are used in section Section 7 where guidance is provided to future document authors.

3. Tag Prefixes

All tags have a prefix indicating who owns their definition. An IANA registry is used to support standardizing tag prefixes. Currently 3 prefixes are defined with all others reserved.

3.1. IETF Standard Tags

An IETF standard tag is a tag that has the prefix "ietf:". All IETF standard tags are registered with IANA in a registry defined later in this document.

3.2. Vendor Tags

A vendor tag is a tag that has the prefix "vendor:". These tags are defined by the vendor that implements the module, and are not standardized; however, it is RECOMMENDED that the vendor include extra identification in the tag name to avoid collisions such as using the enterpise or organization name in the second field (e.g., vendor:example.com:system-management:...).

3.3. Local Tags

A local tag is any tag that has the prefix "local:". These tags are defined by the local user/administrator and will never be standardized.

3.4. Reserved Tags

Any tag not starting with the prefix "ietf:", "vendor:" or "local:" is reserved for future standardization.

4. Tag Management

Tags can become associated with a module in a number of ways. Tags may be defined and associated at model design time, at implementation time, or via user administrative control. As the main consumer of tags are users, users may also remove any tag, no matter how the tag became associated with a module.

4.1. Module Definition Association

A module definition SHOULD indicate a set of tags to be automatically added by the module implementer. If the module definition will be standard the tags MUST also be standard tags (Section 3.1). Thus, new modules can drive the addition of new standard tags to the IANA registry, and the IANA registry can serve as a check against duplication.

4.2. Implementation Association

An implementation MAY include additional tags associated with a module. These tags may be standard or vendor specific tags.

4.3. Administrative Tagging

Tags of any kind can be assigned and removed with normal configuration mechanisms.

Implementations MUST ensure that a modules tag list is consistent across any location from which the list is accessible. So if a user adds a tag through configuration that tag should also be seen when using any augmentation that exposes the modules tag list.

5. Tags Module Structure

5.1. Tags Module Tree

The tree associated with the tags module is:

module: ietf-module-tags
    +--rw module-tags* [name]
       +--rw name          yang:yang-identifier
       +--rw tag*          string
       +--rw masked-tag*   string

5.2. Tags Module

<CODE BEGINS> file "ietf-module-tags@2018-03-06.yang"
module ietf-module-tags {
  yang-version "1";
  namespace "urn:ietf:params:xml:ns:yang:ietf-module-tags";
  prefix "mtags";

  import ietf-yang-types {
    prefix yang;
  }

  organization "IETF NetMod Working Group (NetMod)";

  contact
    "NetMod Working Group - <netmod@ietf.org>";

  description
    "This module describes a tagging mechanism for yang module.
     Tags may be IANA assigned or privately defined types.";

  revision "2018-03-06" {
    description
      "Initial revision.";
    reference "TBD";
  }

  list module-tags {
    key "name";

    description
      "A list of modules and their associated tags";

    leaf name {
        type yang:yang-identifier;
        mandatory true;
        description
            "The YANG module or submodule name.";
    }

    leaf-list tag {
        type string;

        description
            "A tag associated with the module. See the IANA 'YANG Module
             Tag Prefix' registry for reserved prefixes and the IANA
             'YANG Module IETF Tag' registry for IETF standard tags.

             The operational view of this list will contain all
             user-configured tags as well as any predefined tags that
             have not been masked by the user using the masked-tag leaf
             list below.";
    }

    leaf-list masked-tag {
        type string;

        description
            "The list of tags that should not be associated with this
             module. This user can remove (mask) predefined tags by
             adding them to this list. It is not an error to add tags to
             this list that are not predefined for the module.";
    }
  }
}
<CODE ENDS>

6. Other Classifications

It's worth noting that a different yang module classification document exists [RFC8199]. That document is classifying modules in only a logical manner and does not define tagging or any other mechanisms. It divides yang modules into 2 categories (service or element) and then into one of 3 origins: standard, vendor or user. It does provide a good way to discuss and identify modules in general. This document defines standard tags to support [RFC8199] style classification.

7. Guidelines to Model Writers

This section updates [I-D.ietf-netmod-rfc6087bis].

7.1. Define Standard Tags

        module example-module {
          ...
          description
            "[Text describing the module...]

            RFC<this document> TAGS:
            The following tags MUST be included by an implementation:
                 - ietf:some-required-tag:foo
                 - ...
            The following tags SHOULD be included by an implementation:
                 - ietf:some-recommended-tag:bar
                 - ...
            The following tags MAY be included by an implementation:
                 - ietf:some-optional-tag:baz
                 - ...
              ";
          ...
        }

            

A module SHOULD indicate, in the description statement of the module, a set of tags that are to be associated with it. This description should also include the appropriate conformance statement or statements, using [RFC2119] language for each tag.

One SHOULD only include conformance text if there will be tags listed (i.e., there's no need to indicate an empty set).

The module writer may use existing standard tags, or use new tags defined in the model definition, as appropriate. New tags should be assigned in the IANA registry defined below, see Section 8.2 below.

8. IANA Considerations

8.1. YANG Module Tag Prefix Registry

This registry allocates tag prefixes. All YANG module tags SHOULD begin with one of the prefixes in this registry.

The allocation policy for this registry is Specification Required [RFC5226].

 prefix    description
 --------  ---------------------------------------------------
 ietf:     IETF Standard Tag allocated in the IANA YANG Module
           IETF Tag Registry.
 vendor:   Non-standardized tags allocated by the module implementer.
 local:    Non-standardized tags allocated by and for the user.
            

The initial values for this registry are as follows.

Other SDOs (standard organizations) wishing to standardize their own set of tags could allocate a top level prefix from this registry.

8.2. YANG Module IETF Tag Registry

This registry allocates prefixes that have the standard prefix "ietf:". New values should be well considered and not achievable through a combination of already existing standard tags.

The allocation policy for this registry is IETF Review [RFC5226].

The initial values for this registry are as follows.

[Editor's note: many of these tags may move to [I-D.ietf-rtgwg-device-model] if/when that document is refactored to use tags.]

9. References

9.1. Normative References

9.2. Informative References

Authors' Addresses