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Network Working Group J. Snell Internet-DraftFebruaryMarch 2006 Expires:August 5,September 2, 2006Feed Thread: Enabling Threaded Entries inAtomdraft-snell-atompub-feed-thread-06.txtThreading 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 onAugust 5,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 ExpiresAugust 5,September 2, 2006 [Page 1] Internet-Draft Feed ThreadFebruaryMarch 2006 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 3 3. The 'in-reply-to' extension element . . . . . . . . . . . . . 3 4. The 'replies' link relation . . . . . . . . . . . . . . . . .65 5. Security Considerations . . . . . . . . . . . . . . . . . . .87 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . .87 7. References . . . . . . . . . . . . . . . . . . . . . . . . . .97 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . .97 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . .109 Intellectual Property and Copyright Statements . . . . . . . . . .1110 Snell ExpiresAugust 5,September 2, 2006 [Page 2] Internet-Draft Feed ThreadFebruaryMarch 2006 1. Introduction This document specifiesa mechanism that allows the expression ofextension 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.In this specification, "entry" refers to an atom:entry element. In this specification, "feed" refers to an Atom Feed Document. In this specification, "head section" refers to the children of a feed's document-wide metadata container; e.g., the child elements of the atom:feed element in an Atom Feed Document. In this specification, "link" refers to the atom:link element. In this specification, "link relation" refers to the value of the atom:link element's rel attribute. In this specification, the term "extension element" refers to a structured extension element as described in [RFC4287].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'id''ref' and 'href' attributes.Snell Expires August 5, 2006 [Page 3] Internet-Draft Feed Thread February 2006in-reply-to = element thr:in-reply-to { atomCommonAttributes, attributeidref { atomURI }?, attribute href { atomURI }?, attribute type { atomMediaType }?, attribute source { atomURI }? } The'id''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 valueidentifiesspecifies the IRI of an Atom Feed Document within which an atom:entry representing the resource being responded to MAY be found.o atom:entry elements MAY contain any number of 'in-reply-to' extension elements. o atom:entry elements SHOULD NOT contain more than one 'in-reply-to' extension element having the same 'id' attribute value. o atom:feed elements MAY contain any number of 'in-reply-to' extension elements. o atom:feed elements SHOULD NOT contain more than one 'in-reply-to' extension elements having the same 'id' attribute value. o atom:sourceAtom feed, entry and source elements MAY each contain any number of 'in-reply-to' extensionelements. o atom:sourceelements but SHOULD NOT contain more than one'in-reply-to' extension elementhaving the same'id''ref' and 'href' attributevalue. Snell Expires August 5, 2006 [Page 4] Internet-Draft Feed Thread February 2006values. 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</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-toid="tag:entries.com,2005:1"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>In order toTo allow Atom clients that are not familiar with thein- reply-to elementin-reply-to extension to know that a relationship exists between thecontainingentry 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 ExpiresAugust 5,September 2, 2006 [Page5]4] Internet-Draft Feed ThreadFebruaryMarch 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-toid="tag:example.org,2005:1,0"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 toentriesan atom:entry MAY appear within the same feed document as theentryresource being responded to, it is common practice to separate responses into a separate feeddocumentdocuments or other resource. In such cases, it is helpful for an atom:feed or atom:entry to indicate the locationof a resourcewhere responses may be found.For this purpose,An atom:link element with the'replies' link relation is used. The type'rel' attributeof the 'replies' link relation indicates the type of resource containing the responses. Avalueof 'application/ atom+xml' indicates that the resource identified by the link's href attribute'replies' iseither an Atom Feed Document or an Atom Entry Document that MAY contain one or more 'in-reply-to' link relations.used for this purpose. If the type attribute of the atom:link is omitted, it's value is assumed to be"application/ atom+xml". o atom:entry"application/atom+xml". Atom feed, entry and source elements MAY each contain any number of 'replies'link relations. Snell Expires August 5, 2006 [Page 6] Internet-Draft Feed Thread February 2006 o atom:entry elements MUST NOT contain more than one 'replies' link relation having the same 'type' and 'href' attribute values. o atom:feed elements MAY contain any number of 'replies' link relations. o atom:feed elements MUST NOT contain more than one 'replies' link relation having the same 'type' and 'href' attribute values. o atom:source elements MAY contain any number of 'replies' link relations. o atom:sourceatom:link elementsMUSTbut SHOULD NOT contain more than one'replies' link relationhaving the same 'type' and 'href' attribute values. A 'replies' linkrelationappearing as a child ofan atom:feedthe Atom feed oratom:sourcesource element indicates that the referenced resource MAY contain responses to any of theFeed contained atom:entry's.feeds entries. A 'replies' linkrelationappearing as a child of anatom:entryAtom entry element indicates that the referenced resource MAY contain responses specific tothe containing atom:entry.that entry. Snell Expires September 2, 2006 [Page 5] Internet-Draft Feed Thread March 2006 Atomlink elements specifyinglinks 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.The "replies" linkReply 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 Constructfrom [RFC4287]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.The presence of a 'replies' link relation 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. Snell Expires August 5, 2006 [Page 7] Internet-Draft Feed Thread February 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" thr:count="10" thr:when="2006-02-20T00:00:00Z" /> <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. Security Considerations Feeds usingImplementors should note that while themechanisms described here could be crafted inAtom 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 sucha wayextensions. The result of this is that the thr:count and thr:when attributes fall outside of the guidelines for Atom extensions asto 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). This risk can be mitigated by requiring user intervention after a certain numberdefined in Section 6 ofrequests, or[RFC4287] and may not be supported bylimiting requests either accordingall Atom implementations. 5. Security Considerations As this specification defines an extension toa hard limit,the Atom Syndication Format, it is subject to the same security considerations as defined in [RFC4287] and does not introduce any new orwith heuristics.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].Snell Expires August 5, 2006 [Page 8] Internet-Draft Feed Thread February 2006Attribute 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 ExpiresAugust 5,September 2, 2006 [Page9]8] Internet-Draft Feed ThreadFebruaryMarch 2006 Author's Address James M Snell Phone: Email: jasnell@gmail.com URI:http://snellspace.comhttp://www.snellspace.com Snell ExpiresAugust 5,September 2, 2006 [Page10]9] Internet-Draft Feed ThreadFebruaryMarch 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 ExpiresAugust 5,September 2, 2006 [Page11]10] ----