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Keywords: atom syndication format, atom feeds, atom entries
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
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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.
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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" />
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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
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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.
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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>.
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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
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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
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rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
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