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Network Working Group J. Snell Internet-DraftAprilMay 12, 2006 Expires:October 3,November 13, 2006 Atom Threading Extensionsdraft-snell-atompub-feed-thread-09.txtdraft-snell-atompub-feed-thread-10.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 onOctober 3,November 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 ExpiresOctober 3,November 13, 2006 [Page 1] Internet-Draft Feed ThreadAprilMay 2006 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 3 3. The 'in-reply-to' extension element . . . . . . . . . . . . . 3 4. The 'replies' link relation . . . . . . . . . . . . . . . . . 6 5.The 'thr:replies' Element . . . . . . . . . . . . . . . . . . 7 6.Security Considerations . . . . . . . . . . . . . . . . . . .9 7.7 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . .10 8.8 7. References . . . . . . . . . . . . . . . . . . . . . . . . . .10 8.1.8 7.1. Normative References . . . . . . . . . . . . . . . . . . .10 8.2.8 7.2. Informative References . . . . . . . . . . . . . . . . . .118 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . .119 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . .1210 Intellectual Property and Copyright Statements . . . . . . . . . .1311 Snell ExpiresOctober 3,November 13, 2006 [Page 2] Internet-Draft Feed ThreadAprilMay 2006 1. Introduction This document defines an 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. The XML Namespaces URI [W3C.REC-xml-names-19990114] for the XML elements and attributes described in this specification is: http://purl.org/syndication/thread/1.0 In this document, the namespace prefix "thr:" is used for the above Namespace URI. Note that the choice of namespace prefix is arbitrary and not semantically significant. This specification uses a shorthand form of terms from the XML Infoset [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]. In those sections this specification uses the atomCommonAttributes, atomMediaType and atomURI patterns defined in [RFC4287]. However, the text of this specification provides the sole 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"extensionelement is used to indicate thata feedan entry is a response to anotherresource. The elementresource and MUST contain either or both the "ref" and "href" attributes. Snell ExpiresOctober 3,November 13, 2006 [Page 3] Internet-Draft Feed ThreadAprilMay 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" attribute specifies the universally unique identifier of the resource being responded to. The valueof the attributeMUST conform to the same construction and comparison rules as the value of the atom:id element. The "source" attribute MAY be used to specify the IRI [RFC3987] of an Atom Feed or Entry Documentwithin whichcontaining anatom: entryatom:entry with an atom:id value equal to thevalue of the"ref"attribute may be found.attribute. The "href" attribute specifiesanthe IRI that may be used to retrieve a representation of the resource being responded to. The "type" attribute MAY be used to identify the media type [RFC4288] of the resource identified by the "href" attribute. Atomfeed, entry and source elementsentries MAYeachcontain any number of "in-reply-to" extensionelements but SHOULD NOT contain more than one having the same "ref" value.elements. Snell ExpiresOctober 3,November 13, 2006 [Page 4] Internet-Draft Feed ThreadAprilMay 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 ExpiresOctober 3,November 13, 2006 [Page 5] Internet-Draft Feed ThreadAprilMay 2006 Forexampleexample, <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 relationWhile responses to an atom:entryAn Atom link element with a rel attribute value of "replies" mayappear within the same feed document as the resource being responded to, it is common practicebe used toseparate responses intoreference aseparate feed document or other resource. In such cases, it is helpful for an atom:feed or atom:entry to indicate the locationresource where responses to an entry 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 MAYeachcontain any number of"replies" atom:link elements but SHOULD NOT contain more than one having the same "type" and "href" attribute values.replies links. A "replies" link appearing as a child of the Atom feed or source element indicates that thereferencedlinked resource may contain responses to any ofthethat feeds entries. A "replies" link appearing as a child of an Atom entry element indicates that thereferencedlinked resource may contain responses specific to that entry. 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 Snell ExpiresOctober 3,November 13, 2006 [Page 6] Internet-Draft Feed ThreadAprilMay 2006For 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" /> <summary>This is my original entry</summary> </entry> </feed> 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. 5. The 'thr:replies' Element In some cases, a feed publisher may wish to provide additional metadata about a linked Web resource containing replies beyond what the atom:link element allows. For instance, the feed publisher may wish to identify the total number of known replies and the date and time of the most recent reply, etc. The "thr:replies" element provides a container for this metadata. thrReplies = element thr:replies { atomCommonAttributes, attribute ref { atomUri }, attribute label { text }?, attribute count { nonNegativeInteger }?, attribute updated { date-time }? ( extensionElement* ) Snell Expires October 3, 2006 [Page 7] Internet-Draft Feed Thread April 2006 } The "thr:replies" element MUST contain a "ref" attribute whose value is the universaly unique identifier of a Web resource that contains replies to the containing entry. For instance, if a "replies" link relation is used to point to an Atom Feed Document, the "ref" attribute of the corresponding thr:replies element is the value of that Atom Feed Document's atom:id. The value of the attribute MUST conform to the same construction and comparison rules as the atom:id element. Atom entry elements MAY contain zero or more "thr:replies" elements so long as each contains a different ref attribute value. The "thr:replies" element MAY contain a "thr:label" attribute specifying a Language-Sensitive human-readable label. The "thr:replies" element SHOULD contain a "count" attribute whose value is a non-negative integer indicating the total number of replies contained by the identified resource. The value is strictly advisory and may not accuratelyreflect the actual number of replies.The "thr:replies" elementReply links MAY also containan "updated"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 theidentifiedlinked resource. The value is strictly advisory and may not accurately reflect the actual date and time of the most recent reply.The "thr:replies" element MAY contain any number of namespaced extension elements. For instance, an extension to the thr:replies element may be used to identify the URI of an Atom Publishing Protocol collection to which replies can be posted. Such extensions MUST be handled as "Foreign Markup" as defined by [RFC4287]. Snell Expires October 3, 2006 [Page 8] Internet-Draft Feed Thread April 2006For example, <feed xmlns="http://www.w3.org/2005/Atom" xmlns:thr="http://purl.org/syndication/thread/1.0"><id>tag:example.org,2006</id> <title>Entries and Comments</title> ... <entry> <id>tag:example.org,2006:1</id><id>http://www.example.org/myfeed</id> <title>MyPost</title> <updated>2006-05-01T08:08:08Z</updated>Example Feed</title> <updated>2005-07-28T12:00:00Z</updated> <linkrel="replies" href="/comments" type="application/atom+xml" /> <thr:replies ref="tag:example.org,2006:comments" label="Comments and Trackbacks" count="2" updated="2006-05-01T12:12:12Z"/> <thr:replies ref="tag:example.org,2006" label="Follow-ups and Corrections" count="1" updated="2006-05-01T09:09:09Z"href="http://www.example.org/myfeed" />... </entry><author><name>James</name></author> <entry><id>tag:example.org,2006:2</id><id>tag:entries.com,2005:1</id> <title>MySecond Post</title> <updated>2006-05-01T09:09:09Z</updated>original entry</title> <updated>2006-03-01T12:12:12Z</updated> <link href="http://www.example.org/entries/1" /> <link rel="replies"href="/comments"type="application/atom+xml" href="http://www.example.org/mycommentsfeed.xml" thr:count="10" thr:when="2005-07-28T12:10:00Z" /><thr:replies ref="tag:example.org,2006:comments" label="Comments and Trackbacks" count="1" updated="2006-05-01T10:10:10Z" /> <thr:in-reply-to ref="tag:example.org,2006:1" /> ...<summary>This is my original entry</summary> </entry> </feed>Here, the entry identified by the atom:id value "tag:example.og,2006:1" has two replies in the resource identified by the IRI "tag:example.org,2006:comments" and one reply included directly withinThe use of "replies" link relations specifying any media type other than "application/atom+xml" is undefined. Software written to conform to this version of theAtom Feed Document. 6.specification will not be guaranteed to process such links correctly. 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]. Feeds using the mechanisms described here could be crafted in such aSnell Expires October 3, 2006 [Page 9] Internet-Draft Feed Thread April 2006way 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 Snell Expires November 13, 2006 [Page 7] Internet-Draft Feed Thread May 2006 a certain number of requests, or by limiting requests either according to a hard limit, or with heuristics.7.6. 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 5)8.7. References8.1.7.1. 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. [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.Snell Expires October 3, 2006 [Page 10] Internet-Draft Feed Thread April 2006 8.2.7.2. Informative References [RELAXNG] Clark, J., "RELAX NG Compact Syntax", December 2001,<http ://www.oasis-open.org/committees/relax-ng/<http://www.oasis-open.org/committees/relax-ng/ compact-20021121.html>. Snell Expires November 13, 2006 [Page 8] Internet-Draft Feed Thread May 2006 Appendix A. Acknowledgements 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 ExpiresOctober 3,November 13, 2006 [Page11]9] Internet-Draft Feed ThreadAprilMay 2006 Author's Address James M Snell Phone: Email: jasnell@gmail.com URI: http://www.snellspace.com Snell ExpiresOctober 3,November 13, 2006 [Page12]10] Internet-Draft Feed ThreadAprilMay 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 ExpiresOctober 3,November 13, 2006 [Page13]11] ----