Network Working Group J. Snell Internet-Draft March 2006 Expires: September 2, 2006 Atom Threading Extensions draft-snell-atompub-feed-thread-07.txt 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- Drafts. 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 http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on September 2, 2006. Copyright Notice Copyright (C) The Internet Society (2006). Abstract This memo presents a mechanism that allows feeds publishers to express threaded discussions within the Atom Syndication Format. Snell Expires September 2, 2006 [Page 1] Internet-Draft Feed Thread March 2006 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 3 3. The 'in-reply-to' extension element . . . . . . . . . . . . . 3 4. The 'replies' link relation . . . . . . . . . . . . . . . . . 5 5. Security Considerations . . . . . . . . . . . . . . . . . . . 7 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 7 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 9 Intellectual Property and Copyright Statements . . . . . . . . . . 10 Snell Expires September 2, 2006 [Page 2] Internet-Draft Feed Thread March 2006 1. Introduction This document specifies extension for expressing threaded discussions within the Atom Syndication Format ([RFC4287]). 2. 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], as scoped to those conformance targets. This specification uses XML Namespaces [W3C.REC-xml-names-19990114] to uniquely identify XML element names. It uses the following namespace prefix for the indicated namespace URI; "thr": "http://purl.org/syndication/thread/1.0" This specification uses terms from the XML Infoset [W3C.REC-xml- infoset-20040204]. However, this specification uses a shorthand; the phrase "Information Item" is omitted when naming Element Information Items. Therefore, when this specification uses the term "element," it is referring to an Element Information Item in Infoset terms. 3. The 'in-reply-to' extension element The 'in-reply-to' extension element is used to indicate that a feed entry is a response to another resource. The element MUST contain either or both the 'ref' and 'href' attributes. in-reply-to = element thr:in-reply-to { atomCommonAttributes, attribute ref { atomURI }?, attribute href { atomURI }?, attribute type { atomMediaType }?, attribute source { atomURI }? } The 'ref' attribute specifies the universally unique identifier of the resource being responded to. The value of the attribute MUST conform to the same construction and comparison rules as the atom:id element. The 'href' attribute specifies an IRI that may be used to retrieve a representation of the resource being responded to. The "in-reply-to" element MAY contain a "type" attribute whose value identifies the media type of the resource identified by the href attribute. Snell Expires September 2, 2006 [Page 3] Internet-Draft Feed Thread March 2006 The "in-reply-to" element MAY contain a "source" attribute whose value specifies the IRI of an Atom Feed Document within which an atom:entry representing the resource being responded to MAY be found. Atom feed, entry and source elements MAY each contain any number of 'in-reply-to' extension elements but SHOULD NOT contain more than one having the same 'ref' and 'href' attribute values. For example http://www.example.org/myfeed My Example Feed 2005-07-28T12:00:00Z James tag:example.org,2005:1 My original entry 2006-03-01T12:12:12Z This is my original entry tag:example.org,2005:1,1 A response to the original 2006-03-01T12:12:12Z This is a response to the original entry To allow Atom clients that are not familiar with the in-reply-to extension to know that a relationship exists between the entry and the resource being responded to, publishers are advised to consider including a "related" link referencing a representation of the resource identified by the in-reply-to element. Snell Expires September 2, 2006 [Page 4] Internet-Draft Feed Thread March 2006 For example http://www.example.org/myfeed My Example Feed 2005-07-28T12:00:00Z James tag:example.org,2005:1,1 A response to the original 2006-03-01T12:12:12Z This is a response to the original entry 4. The 'replies' link relation While responses to an atom:entry MAY appear within the same feed document as the resource being responded to, it is common practice to separate responses into a separate feed documents or other resource. In such cases, it is helpful for an atom:feed or atom:entry to indicate the location where responses may be found. An atom:link element with the 'rel' attribute value 'replies' is used for this purpose. If the type attribute of the atom:link is omitted, it's value is assumed to be "application/atom+xml". Atom feed, entry and source elements MAY each contain any number of 'replies' atom:link elements but SHOULD NOT contain more than one having the same 'type' and 'href' attribute values. A 'replies' link appearing as a child of the Atom feed or source element indicates that the referenced resource MAY contain responses to any of the feeds entries. A 'replies' link appearing as a child of an Atom entry element indicates that the referenced resource MAY contain responses specific to that entry. Snell Expires September 2, 2006 [Page 5] Internet-Draft Feed Thread March 2006 Atom links using the "replies" rel attribute value MAY contain a "thr:count" attribute whose value is a non-negative integer indicating the total number of replies contained by the linked resource. The value is strictly advisory and may not accurately reflect the actual number of replies. Reply links MAY also contain a "thr:when" attribute whose value is a [RFC3339] date-time stamp conforming to the same construction rules as the Atom Date Construct defined in [RFC4287], and is used to indicate the date and time of the most recent reply contained by the linked resource. The value is strictly advisory and may not accurately reflect the actual date and time of the most recent reply. For example, replies contained in a separate Atom feed http://www.example.org/myfeed My Example Feed 2005-07-28T12:00:00Z James tag:entries.com,2005:1 My original entry 2006-03-01T12:12:12Z This is my original entry The presence of a 'replies' link is merely a hint as to where responses to entries MAY be found and does not guarantee that the referenced resource contains any responses to any entries within the containing feed. The behavior of 'replies' link relations specifying any media type other than "application/atom+xml" is undefined. Software written to conform to this version of the specification will not be guaranteed to process such links correctly. Implementors should note that while the Atom Syndication Format does not forbid the inclusion of namespaced extension attributes on the Snell Expires September 2, 2006 [Page 6] Internet-Draft Feed Thread March 2006 Atom link element, neither does is explicitly allow for such extensions. The result of this is that the thr:count and thr:when attributes fall outside of the guidelines for Atom extensions as defined in Section 6 of [RFC4287] and may not be supported by all Atom implementations. 5. Security Considerations As this specification defines an extension to the Atom Syndication Format, it is subject to the same security considerations as defined in [RFC4287] and does not introduce any new or specific considerations. 6. IANA Considerations This specification defines one new Atom link relation type to be registered in the IANA Registry of Link Relation as defined by [RFC4287]. Attribute Value: replies Description: (see section 4) Expected display characteristics: (see section 4) Security considerations: (see section 6) 7. References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet: Timestamps", RFC 3339, July 2002. [RFC4287] Nottingham, M. and R. Sayre, "The Atom Syndication Format", RFC 4287, December 2005. [W3C.REC-xml-infoset-20040204] Tobin, R. and J. Cowan, "XML Information Set (Second Edition)", W3C REC REC-xml-infoset-20040204, February 2004. [W3C.REC-xml-names-19990114] Hollander, D., Bray, T., and A. Layman, "Namespaces in XML", W3C REC REC-xml-names-19990114, January 1999. Appendix A. Acknowledgements Snell Expires September 2, 2006 [Page 7] Internet-Draft Feed Thread March 2006 The author gratefully acknowledges the feedback from James Holderness, Byrne Reese, Aristotle Pagaltzis, and the remaining members of the Atom Publishing Format and Protocol working group during the development of this specification. Snell Expires September 2, 2006 [Page 8] Internet-Draft Feed Thread March 2006 Author's Address James M Snell Phone: Email: jasnell@gmail.com URI: http://www.snellspace.com Snell Expires September 2, 2006 [Page 9] Internet-Draft Feed Thread March 2006 Intellectual Property Statement 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. Disclaimer of Validity 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 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. Copyright Statement Copyright (C) The Internet Society (2006). 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. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Snell Expires September 2, 2006 [Page 10]