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Atom License Extension

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 4946.
Author James M. Snell
Last updated 2015-10-14 (Latest revision 2007-03-28)
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status Experimental
Stream WG state (None)
Document shepherd (None)
IESG IESG state Became RFC 4946 (Experimental)
Action Holders
Consensus boilerplate Unknown
Telechat date (None)
Responsible AD Lisa M. Dusseault
Send notices to (None)
Network Working Group                                           J. Snell
Internet-Draft                                            March 28, 2007
Intended status: Standards Track
Expires: September 29, 2007

                         Atom License Extension

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at

   This Internet-Draft will expire on September 29, 2007.

Copyright Notice

   Copyright (C) The IETF Trust (2007).


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

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.1.  Notational Conventions  . . . . . . . . . . . . . . . . . . 3
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  The "license" link relation . . . . . . . . . . . . . . . . . . 4
     2.1.  Unspecified License Links . . . . . . . . . . . . . . . . . 4
     2.2.  Comparing License Links . . . . . . . . . . . . . . . . . . 4
     2.3.  Example . . . . . . . . . . . . . . . . . . . . . . . . . . 5
     2.4.  Inherited Licenses  . . . . . . . . . . . . . . . . . . . . 5
     2.5.  Relationship with the "atom:rights" element . . . . . . . . 6
   3.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   5.  Normative References  . . . . . . . . . . . . . . . . . . . . . 7
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . . . 7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 7
   Intellectual Property and Copyright Statements  . . . . . . . . . . 8

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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",
   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 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 which must be assumed by those exercising those

   Atom allows the use of 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

   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

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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
   "") to indicate that a
   feed or license has not been explicitly linked to a license

   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 it's fully
   qualified form before comparison.

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2.3.  Example

     <feed xmlns="">
       <title>My Example Feed</title>
       <link href="" />
       <link rel="license" type="application/rdf+xml"
         href="" />
         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 under the
         Creative Commons Attribute License.
         <title>Atom Powered Robots Run Amok</title>
         <link href="" />
         <summary>Atom Powered Robots Run Amok</summary>
         <author><name>Jane Smith</name></author>
         <link rel="license" type="text/html"
           href="" />

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 as 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 entries 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. search for entries containing pictures and the word "knitting"

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   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
   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 which 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 which do not already contain atom:source

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
       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.

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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.

   [RFC4287]  Nottingham, M., Ed. and R. Sayre, Ed., "The Atom
              Syndication Format", RFC 4287, December 2005.

              Marsh, J., "XML Base", World Wide Web Consortium
              Recommendation REC-xmlbase-20010627, June 2001,

Appendix A.  Acknowledgements

   The author gratefully acknowledges the feedback from Mike Linksvayer,
   Robin Cover, Lisa Dussealt, 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


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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

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

   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


   Funding for the RFC Editor function is provided by the IETF
   Administrative Support Activity (IASA).

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