Atom License Extension
RFC 4946

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Network Working Group                                           J. Snell
Request for Comments: 4946                                     July 2007
Category: Experimental

                         Atom License Extension

Status of This Memo

   This memo defines an Experimental Protocol for the Internet
   community.  It does not specify an Internet standard of any kind.
   Discussion and suggestions for improvement are requested.
   Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   This memo defines an extension to the Atom Syndication Format for
   describing licenses associated with Atom feeds and entries.

Table of Contents

   1. Introduction ....................................................2
      1.1. Notational Conventions .....................................2
      1.2. Terminology ................................................2
   2. The "license" Link Relation .....................................3
      2.1. Unspecified License Links ..................................3
      2.2. Comparing License Links ....................................3
      2.3. Example ....................................................3
      2.4. Inherited Licenses .........................................4
      2.5. Relationship with the atom:rights Element ..................4
   3. Security Considerations .........................................5
   4. IANA Considerations .............................................5
   5. Normative References ............................................5
   Appendix A.  Acknowledgements ......................................7

Snell                         Experimental                      [Page 1]
RFC 4946                 Atom License Extension                July 2007

1.  Introduction

   This document defines an extension to the Atom Syndication Format
   that can be used to add links to Atom feed or entry documents
   referencing resources that describe the explicit rights that have
   been granted to consumers of those documents.

   Describing licenses using the mechanisms defined in this
   specification is currently considered to be largely experimental.
   While it is a common practice for feed publishers to associate
   licenses with syndicated content, there are still very few feed
   consumers that utilize such metadata, and the effectiveness of doing
   so is still largely unknown.  As it is not yet certain how these
   mechanisms will be used, implementations and feedback are encouraged.

1.1.  Notational Conventions

   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 BCP 14, [RFC2119].

1.2.  Terminology

   The term "link relation" refers to the value of the Atom link
   elements rel attribute as defined in Section 4.2.7.2 of [RFC4287].

   The term "license" refers to a potentially machine-readable
   description of explicit rights that have been granted to consumers of
   an Atom feed or entry.  Rights granted by a license may be associated
   with obligations that must be assumed by those exercising those
   rights.

   Atom allows the use of Internationalized Resource Identifiers (IRIs)
   [RFC3987].  Every URI [RFC3986] is also an IRI, so a URI may be used
   wherever below an IRI is named.  When an IRI that is not also a URI
   is given for dereferencing, it MUST be mapped to a URI using the
   steps in Section 3.1 of [RFC3987].

   Atom allows the use of the xml:base attribute [W3C.REC-xmlbase-
   20010627] to establish the base URI (or IRI) used to resolve any
   relative references as described in Section 5.1.1 of [RFC3986].

   Atom allows the use of the xml:lang attribute to indicate the natural
   language of an element, its attributes, and its descendents.  The
   language context is only significant for elements and attributes
   declared to be "Language-Sensitive" as described in [RFC4287].  The
   title attribute of the atom:link element is defined as being
   Language-Sensitive.

Snell                         Experimental                      [Page 2]
RFC 4946                 Atom License Extension                July 2007

2.  The "license" Link Relation

   The "license" link relation can be used to associate licenses with a
   feed or entry.

   Feed and entry elements MAY contain any number of "license" link
   relations but MUST NOT contain more than one with the same
   combination of href and type attribute values.  The IRI specified by
   the link's href attribute SHOULD be dereferenceable to return a
   representation of the license.  The license representation MAY be
   machine readable.

   Feeds and entries can be dual-licensed by including multiple
   "license" link relations specifying different href attribute values.
   If multiple "license" link relations are specified, each SHOULD
   contain a title attribute specifying a human-readable label for the