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rfc:rfc4946

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
 license.

2.1. Unspecified License Links

 A publisher can use an "unspecified license link" (a "license" link
 relation with an href attribute value equal to
 "http://purl.org/atompub/license#unspecified") to indicate that a
 feed or license has not been explicitly linked to a license
 description.
 A feed or entry containing an unspecified license link MUST NOT
 contain any other "license" link relations.

2.2. Comparing License Links

 Atom implementations that are capable of supporting "license" links
 SHOULD use the simple string-comparison method described in
 [RFC3987], Section 5.3.1, to determine whether multiple "license"
 links are equivalent.  The other comparison methods discussed in
 Section 5.1 of the IRI specification MAY be used.  If the "license"
 link is specified using a relative reference, it MUST be converted to
 its fully qualified form before comparison.

2.3. Example

   <feed xmlns="http://www.w3.org/2005/Atom">
     <id>http://www.example.com/myfeed</id>
     <title>My Example Feed</title>
     <updated>2005-07-28T12:00:00Z</updated>
     <link href="http://www.example.com/myfeed" />
     <link rel="license" type="application/rdf+xml"
       href="http://creativecommons.org/licenses/by-nc/2.5/rdf" />

Snell Experimental [Page 3] RFC 4946 Atom License Extension July 2007

     <rights>
       Copyright (c) 2005.  Some rights reserved.  This feed
       is licensed under a Creative Commons Attribute-NonCommercial
       Use License.  It contains material originally published by
       Jane Smith at http://www.example.com/entries/1 under the
       Creative Commons Attribute License.
     </rights>
     <author><name>James</name></author>
     <entry>
       <id>tag:entries.org,2005:1</id>
       <title>Atom Powered Robots Run Amok</title>
       <updated>2005-06-28T12:00:00Z</updated>
       <link href="http://www.example.org/entries/1" />
       <summary>Atom Powered Robots Run Amok</summary>
       <author><name>Jane Smith</name></author>
       <link rel="license" type="text/html"
         href="http://creativecommons.org/licenses/by/2.5/" />
     </entry>
   </feed>

2.4. Inherited Licenses

 "License" links specified within atom:feed or atom:source elements
 are inherited by entries.  Generally, a more specific license
 overrides a less specific license.  More specifically, if an
 atom:entry has any "license" link relations, including the
 "undefined" license, it does not inherit any license from a
 containing atom:feed element or contained atom:source element.  If an
 entry has no "license" link relations, and contains an atom:source
 element, it inherits licenses from the atom:source.  If the
 atom:source element contains no "license" links, or if the entry does
 not have an atom:source element, the entry inherits licenses from the
 containing atom:feed.
 An entry's license MAY be inherited by media resources associated
 with the entry.  Some media types have ways of including license
 information, which always overrides the entry's licensing.
 An agent searching to find entries that fall under a specific license
 (e.g. a search for entries containing pictures and the word
 "knitting" where the entry is under any Creative Commons license)
 MUST check the most granular license definition available, rather
 than assume license inheritance without checking.

2.5. Relationship with the atom:rights Element

 "License" link relations are related to the atom:rights element in
 that both are intended to communicate information about the rights

Snell Experimental [Page 4] RFC 4946 Atom License Extension July 2007

 associated with an Atom document.  Where the two differ, however, is
 in the fact that atom:rights is intended strictly as a human-
 readable assertion of rights held over a work while the "license"
 link relation is intended to provide a potentially machine-readable
 description of what rights have been granted to others.  The two
 constructs may overlap one another and conflicts could arise if they
 are contradictory.  It is important that publishers of Atom documents
 ensure that the atom:rights and "license" link relations are
 consistent with one another.
 If an atom:entry that does not contain an atom:source is copied from
 one feed into another feed, then if the feed into which it is copied
 contains a license, an atom:source element SHOULD be added to the
 copied entry.  If a source feed contains a license, that license
 SHOULD be preserved in an atom:source element added to any entries
 copied from the source feed that do not already contain atom:source
 elements.

3. Security Considerations

 When "license" link relations are used in Atom documents, the
 security considerations specified in [RFC4287] Section 8 apply.

4. IANA Considerations

 This specification defines one new Atom link relation type to be
 registered in the IANA Registry of Link Relations as defined by
 [RFC4287].
     Attribute Value: license
     Description: Specifies the IRI of a license associated with
                  the containing feed, entry, or source element.
     Expected display characteristics: None
     Security considerations: When "license" link relations are used
                  in Atom documents, the security considerations for
                  handling links in Atom documents apply.

5. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
            Resource Identifier (URI): Generic Syntax", STD 66, RFC
            3986, January 2005.
 [RFC3987]  Duerst, M. and M. Suignard, "Internationalized Resource
            Identifiers (IRIs)", RFC 3987, January 2005.

Snell Experimental [Page 5] RFC 4946 Atom License Extension July 2007

 [RFC4287]  Nottingham, M., Ed., and R. Sayre, Ed., "The Atom
            Syndication Format", RFC 4287, December 2005.
 [W3C.REC-xmlbase-20010627]
            Marsh, J., "XML Base", World Wide Web Consortium
            Recommendation REC-xmlbase-20010627, June 2001,
            <http://www.w3.org/TR/2001/REC-xmlbase-20010627>.

Snell Experimental [Page 6] RFC 4946 Atom License Extension July 2007

Appendix A. Acknowledgements

 The author gratefully acknowledges the feedback from Mike Linksvayer,
 Robin Cover, Lisa Dusseault, Bjorn Hohrmann, Frank Ellermann, and the
 members of Atom Publishing Format and Protocol working group during
 the development of this specification.

Author's Address

 James M Snell
 EMail: jasnell@gmail.com
 URI:   http://www.snellspace.com

Snell Experimental [Page 7] RFC 4946 Atom License Extension July 2007

Full Copyright Statement

 Copyright (C) The IETF Trust (2007).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
 This document and the information contained herein are provided on an
 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Intellectual Property

 The IETF takes no position regarding the validity or scope of any
 Intellectual Property Rights or other rights that might be claimed to
 pertain to the implementation or use of the technology described in
 this document or the extent to which any license under such rights
 might or might not be available; nor does it represent that it has
 made any independent effort to identify any such rights.  Information
 on the procedures with respect to rights in RFC documents can be
 found in BCP 78 and BCP 79.
 Copies of IPR disclosures made to the IETF Secretariat and any
 assurances of licenses to be made available, or the result of an
 attempt made to obtain a general license or permission for the use of
 such proprietary rights by implementers or users of this
 specification can be obtained from the IETF on-line IPR repository at
 http://www.ietf.org/ipr.
 The IETF invites any interested party to bring to its attention any
 copyrights, patents or patent applications, or other proprietary
 rights that may cover technology that may be required to implement
 this standard.  Please address the information to the IETF at
 ietf-ipr@ietf.org.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Snell Experimental [Page 8]

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