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Network Working Group J. Snell Internet-DraftMarchApril 11, 2006 Expires:September 2,October 13, 2006 Atom Threading Extensionsdraft-snell-atompub-feed-thread-07.txtdraft-snell-atompub-feed-thread-08.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 onSeptember 2,October 13, 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 ExpiresSeptember 2,October 13, 2006 [Page 1] Internet-Draft Feed ThreadMarchApril 2006 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 3 3. The 'in-reply-to' extension element . . . . . . . . . . . . . 3 4. The 'replies' link relation . . . . . . . . . . . . . . . . .56 5. Security Considerations . . . . . . . . . . . . . . . . . . .78 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . .78 7. References . . . . . . . . . . . . . . . . . . . . . . . . . .78 7.1. Normative References . . . . . . . . . . . . . . . . . . . 8 7.2. Informative References . . . . . . . . . . . . . . . . . . 9 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . .79 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . .910 Intellectual Property and Copyright Statements . . . . . . . . . .1011 Snell ExpiresSeptember 2,October 13, 2006 [Page 2] Internet-Draft Feed ThreadMarchApril 2006 1. Introduction This documentspecifiesdefines an extension for expressing threaded discussions within the Atom Syndication Format([RFC4287]).[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 usesThe XML Namespaces URI [W3C.REC-xml-names-19990114]to uniquely identifyfor the XMLelement names. It useselements and attributes described in this specification is: http://purl.org/syndication/thread/1.0 In this document, thefollowingnamespace prefix "thr:" is used for theindicated namespace URI; "thr": "http://purl.org/syndication/thread/1.0"above Namespace URI. This specification uses a shorthand form of terms from the XML Infoset[W3C.REC-xml- infoset-20040204]. However, this specification uses a shorthand; the[W3C.REC-xml-infoset-20040204]. The phrase "Information Item" is omitted when naming Element and Attribute Information Items. Therefore, when this specification uses the term "element," it is referring to an Element Information Item in Infoset terms. Likewise, when this specification uses the term "attribute," it is referring to an Attribute Information Item. Some sections of this specification are illustrated with a non- normative RELAX NG Compact schema [RELAXNG]. However, the text of this specification provides the definition of conformance. This specification uses the atomCommonAttributes, atomURI, and atomMediaType constructs as defined in [RFC4287]. 3. The 'in-reply-to' extension element The'in-reply-to'"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'"ref" and'href'"href" attributes. Snell Expires October 13, 2006 [Page 3] Internet-Draft Feed Thread April 2006 in-reply-to = element thr:in-reply-to { atomCommonAttributes, ( ref, source? | href, type? | ref, source?, href, type? ) } ref = attribute ref { atomURI}?,} href = attribute href { atomURI}?,} type = attribute type { atomMediaType}?,} source = attribute source { atomURI}?} The'ref'"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'"source" attribute MAY be used to specify the IRI [RFC3987] of an Atom Feed or Entry Document within which an atom: entry with an atom:id value equal to the value of the "ref" attribute may be found. 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" attributewhose value identifiesMAY be used to identify the media type [RFC4288] of the resource identified by thehref"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'"in-reply-to" extension elements but SHOULD NOT contain more than one having the same'ref' and 'href' attribute values. For"ref" value. Snell Expires October 13, 2006 [Page 4] Internet-Draft Feed Thread April 2006 An example entry with a response, <feed xmlns="http://www.w3.org/2005/Atom" xmlns:thr="http://purl.org/syndication/thread/1.0"> <id>http://www.example.org/myfeed</id> <title>My Example Feed</title> <updated>2005-07-28T12:00:00Z</updated> <link href="http://www.example.org/myfeed" /> <author><name>James</name></author> <entry> <id>tag:example.org,2005:1</id> <title>My original entry</title> <updated>2006-03-01T12:12:12Z</updated> <link type="application/xhtml+xml" href="http://www.example.org/entries/1" /> <summary>This is my original entry</summary> </entry> <entry> <id>tag:example.org,2005:1,1</id> <title>A response to the original</title> <updated>2006-03-01T12:12:12Z</updated> <link href="http://www.example.org/entries/1/1" /> <thr:in-reply-to ref="tag:entries.com,2005:1" type="application/xhtml+xml" href="http://www.example.org/entries/1"/> <summary>This is a response to the original entry</summary> </entry> </feed> 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 ExpiresSeptember 2,October 13, 2006 [Page4]5] Internet-Draft Feed ThreadMarchApril 2006 For example <feed xmlns="http://www.w3.org/2005/Atom" xmlns:thr="http://purl.org/syndication/thread/1.0"> <id>http://www.example.org/myfeed</id> <title>My Example Feed</title> <updated>2005-07-28T12:00:00Z</updated> <link href="http://www.example.org/myfeed" /> <author><name>James</name></author> <entry> <id>tag:example.org,2005:1,1</id> <title>A response to the original</title> <updated>2006-03-01T12:12:12Z</updated> <link href="http://www.example.org/entries/1/1" /> <thr:in-reply-to ref="tag:example.org,2005:1,0" type="application/xhtml+xml" href="http://www.example.org/entries/1" source="http://www.example.org/myfeed" /> <link rel="related" type="application/xhtml+xml" href="http://www.example.org/entries/1" /> <summary>This is a response to the original entry</summary> </entry> </feed> 4. The 'replies' link relation While responses to an atom:entryMAYmay appear within the same feed document as the resource being responded to, it is common practice to separate responses into a separate feeddocumentsdocument 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'"rel" attribute value'replies'"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'"replies" atom:link elements but SHOULD NOT contain more than one having the same'type'"type" and'href'"href" attribute values. A'replies'"replies" link appearing as a child of the Atom feed or source element indicates that the referenced resourceMAYmay contain responses to any of the feeds entries. A'replies'"replies" link appearing as a child of an Atom entry element indicates that the referenced resourceMAYmay contain responses specific to that entry. Snell ExpiresSeptember 2,October 13, 2006 [Page5]6] Internet-Draft Feed ThreadMarchApril 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 <feed xmlns="http://www.w3.org/2005/Atom" xmlns:thr="http://purl.org/syndication/thread/1.0"> <id>http://www.example.org/myfeed</id> <title>My Example Feed</title> <updated>2005-07-28T12:00:00Z</updated> <link href="http://www.example.org/myfeed" /> <author><name>James</name></author> <entry> <id>tag:entries.com,2005:1</id> <title>My original entry</title> <updated>2006-03-01T12:12:12Z</updated> <link href="http://www.example.org/entries/1" /> <link rel="replies" type="application/atom+xml" href="http://www.example.org/mycommentsfeed.xml" thr:count="10" thr:when="2006-02-20T00:00:00Z" /> <summary>This is my original entry</summary> </entry> </feed> The presence of a'replies'"replies" link is merely a hint as to where responses to entriesMAYmay be found and does not guarantee that the referenced resource contains any responses to any entries within the containing feed. The behavior of'replies'"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 ExpiresSeptember 2,October 13, 2006 [Page6]7] Internet-Draft Feed ThreadMarchApril 2006 Atom link element, neither doesisit explicitly allow for such extensions.The result of this is thatAs a result, the thr:count and thr:when attributes falloutside of the guidelines for Atom extensions as defined in Section 6 ofunder what [RFC4287]and may not be supported by all Atom implementations.defines as "unknown foreign markup". 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[RFC4287]. Feeds using the mechanisms described here could be crafted in such a way as to cause a consumer to initiate excessive (or even an unending sequence of) network requests, causing denial of service (either to the consumer, the target server, and/or intervening networks). Consumers can mitigate this risk by requiring user intervention after a certain number of requests, or by limiting requests either according to a hard limit, or with heuristics. Consumers should be mindful of resource limits when storing feed documents; to reiterate, they are notintroduce any newrequired to always store orspecific considerations.reconstruct the feed when conforming to this specification; they only need inform the user when the reconstructed feed is not complete. 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)None Security considerations: (see section6)5) 7. References 7.1. Normative 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. [RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource Identifiers (IRIs)", RFC 3987, January 2005. Snell Expires October 13, 2006 [Page 8] Internet-Draft Feed Thread April 2006 [RFC4287] Nottingham, M. and R. Sayre, "The Atom Syndication Format", RFC 4287, December 2005. [RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and Registration Procedures", BCP 13, RFC 4288, 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. 7.2. Informative References [RELAXNG] Clark, J., "RELAX NG Compact Syntax", December 2001, <http://www.oasis-open.org/committees/relax-ng/ compact-20021121.html>. Appendix A. AcknowledgementsSnell Expires September 2, 2006 [Page 7] Internet-Draft Feed Thread March 2006The 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 ExpiresSeptember 2,October 13, 2006 [Page8]9] Internet-Draft Feed ThreadMarchApril 2006 Author's Address James M Snell Phone: Email: jasnell@gmail.com URI: http://www.snellspace.com Snell ExpiresSeptember 2,October 13, 2006 [Page9]10] Internet-Draft Feed ThreadMarchApril 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 ExpiresSeptember 2,October 13, 2006 [Page10]11] ----