Network Working Group J. Snell Internet-Draft July 2005 Expires: January 2, 2006 Feed Thread: Enabling Threaded Entries in Atom draft-snell-atompub-feed-thread-00.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 January 2, 2006. Copyright Notice Copyright (C) The Internet Society (2005). Abstract This memo presents a mechanism that allows feeds publishers to express threading relationships between entries and feeds. Snell Expires January 2, 2006 [Page 1] Internet-Draft Feed Thread July 2005 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 Author's Address . . . . . . . . . . . . . . . . . . . . . . . 7 A. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8 Intellectual Property and Copyright Statements . . . . . . . . 9 Snell Expires January 2, 2006 [Page 2] Internet-Draft Feed Thread July 2005 1. Introduction This document specifies a mechanism that allows the expression of threaded discussions within the Atom Syndication Format ([I-D.ietf- atompub-format]). 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 [I-D.ietf-atompub- format]. 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 an atom: entry is a response to another resource. The element must take one of two forms as described by the inReplyToDereferenceable and inReplyToNonDereferenceable constructs defined below. Snell Expires January 2, 2006 [Page 3] Internet-Draft Feed Thread July 2005 inReplyToDereferenceable = element thr:in-reply-to { atomCommonAttributes, attribute href { atomURI }, attribute type { atomMediatype }? } inReplyToNonDereferenceable = element thr:in-reply-to { atomCommonAttributes, attribute idref { atomURI }, attribute type { atomMediaType }?, attribute source { atomURI}? } In the inReplyToDereferenceable form, the href attribute MUST specify a dereferenceable URI that may be used to locate the entity that the containing Atom Entry is a response to. The type attribute MAY be used to indicate the media type of the entity specified by the href attribute. In the inReplyToNonDereferenceable form, the idref attribute MUST specify a nondereferenceable URI that uniquely identifies the entity that the containing Atom Entry is a response to. The type attribute MAY be used to indicate the media type of the entity identified by the id attribute. The source attribute MAY be used to specify a dereferenceable URI identifying the source of the entity being responded to. o atom:entry elements MAY contain any number of 'in-reply-to' extension elements. o atom:entry elements MUST NOT contain more than one 'in-reply-to' extension element having the same 'type' and 'href' attribute or 'type' and 'idref' attribute values. o atom:feed elements MAY contain any number of 'in-reply-to' extension elements. o atom:feed elements MUST NOT contain more than one 'in-reply-to' extension elements having the same 'type' and 'href' attribute or 'type' and 'idref' attribute values. o atom:source elements MAY contain any number of 'in-reply-to' extension elements. o atom:source elements MUST NOT contain more than one 'in-reply-to' extension element having the same 'type' and 'href' attribute or 'type' and 'idref' attribute values. o If an atom:entry element does not contain any 'in-reply-to' extension elements, any 'in-reply-to' extension elements of the contained atom:source are considered to apply o In an Atom Feed Document, if an atom:entry element or a contained atom:source element do not contain any 'in-reply-to' extension elements, any 'in-reply-to' extension elements in the feed head Snell Expires January 2, 2006 [Page 4] Internet-Draft Feed Thread July 2005 section are considered to apply. For example http://www.example.com/myfeed My Example Feed 2005-07-28T12:00:00Z James tag:entries.com,2005:1 My original entry This is my original entry tag:entries.com,2005:1,1 A response to the original This is a response to the original entry The behavior of 'in-reply-to' extension elements with type attributes 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. 4. The 'replies' link relation While responses to entries MAY appear within the same feed as the entry being responded to, it is common practice to separate responses into a separate feed document or other resource. In such cases, it is helpful for an atom:feed or atom:entry to indicate the location of a resource where responses may be found. For this purpose, the 'replies' link relation is used. The type attribute of the 'replies' link relation indicates the type of resource containing the responses. A value of 'application/ atom+xml' indicates that the resource identified by the link's href attribute is either an Atom Feed Document or an Atom Entry Document that MAY contain one or more 'in-reply-to' link relations. If the type attribute is omitted, it's value is assumed to be "application/ atom+xml". Snell Expires January 2, 2006 [Page 5] Internet-Draft Feed Thread July 2005 o atom:entry elements MAY contain any number of 'replies' link relations. 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:source elements MUST NOT contain more than one 'replies' link relation having the same 'type' and 'href' attribute values. o If an atom:entry element does not contain any 'replies' link relations, any 'replies' link relations of the contained atom: source are considered to apply o In an Atom Feed Document, if an atom:entry element or a contained atom:source element do not contain any 'replies' link relations, any 'replies' link relations in the feed head section are considered to apply. 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 'in-reply-to' link relations or responses to any entries within the containing feed. For example, replies contained in a separate Atom feed http://www.example.com/myfeed My Example Feed 2005-07-28T12:00:00Z James tag:entries.com,2005:1 My original entry This is my original entry 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. Snell Expires January 2, 2006 [Page 6] Internet-Draft Feed Thread July 2005 5. Security Considerations 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). This risk can be mitigated by requiring user intervention after a certain number of requests, or by limiting requests either according to a hard limit, or with heuristics. 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 [I-D.ietf-atompub-format]. Attribute Value: replies Description: (see section 4) Expected display characteristics: (see section 4) Security considerations: (see section 6) 7. References [I-D.ietf-atompub-format] Sayre, R. and M. Nottingham, "The Atom Syndication Format", draft-ietf-atompub-format-10 (work in progress), July 2005. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [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 January 2, 2006 [Page 7] Internet-Draft Feed Thread July 2005 Author's Address James M Snell Phone: Email: jasnell@gmail.com URI: http://snellspace.com Appendix A. Acknowledgements The author gratefully acknowledges the feedback from the members of Atom Publishing Format and Protocol working group during the development of this specification. Snell Expires January 2, 2006 [Page 8] Internet-Draft Feed Thread July 2005 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. 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Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Snell Expires January 2, 2006 [Page 9]