Network Working Group J. Snell
Internet-Draft February 20, 2006
Expires: August 24, 2006
Feed Thread: Enabling Threaded Entries in Atom
draft-snell-atompub-feed-thread-05.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 August 24, 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 August 24, 2006 [Page 1]
Internet-Draft Feed Thread February 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. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10
Intellectual Property and Copyright Statements . . . . . . . . . . 11
Snell Expires August 24, 2006 [Page 2]
Internet-Draft Feed Thread February 2006
1. Introduction
This document specifies a mechanism that allows the expression of
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' and 'href' attributes.
Snell Expires August 24, 2006 [Page 3]
Internet-Draft Feed Thread February 2006
in-reply-to = element thr:in-reply-to {
atomCommonAttributes,
attribute id { atomURI }?,
attribute href { atomURI }?,
attribute type { atomMediaType }?,
attribute source { atomURI }?
}
The 'id' 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.
The "in-reply-to" element MAY contain a "source" attribute whose
value identifies 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:source elements MAY contain any number of 'in-reply-to'
extension elements.
o atom:source elements SHOULD NOT contain more than one
'in-reply-to' extension element having the same 'id' attribute
value.
Snell Expires August 24, 2006 [Page 4]
Internet-Draft Feed Thread February 2006
For example
http://www.example.org/myfeedMy Example Feed2005-07-28T12:00:00ZJamestag:example.org,2005:1
My original entryThis is my original entrytag:example.org,2005:1,1
A response to the originalThis is a response to the original entry
In order to allow Atom clients that are not familiar with the in-
reply-to element to know that a relationship exists between the
containing 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 August 24, 2006 [Page 5]
Internet-Draft Feed Thread February 2006
For example
http://www.example.org/myfeedMy Example Feed2005-07-28T12:00:00ZJamestag:example.org,2005:1,1
A response to the originalThis is a response to the original entry
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".
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.
Snell Expires August 24, 2006 [Page 6]
Internet-Draft Feed Thread February 2006
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.
A 'replies' link relation appearing as a child of an atom:feed or
atom:source element indicates that the referenced resource MAY
contain responses to any of the Feed contained atom:entry's. A
'replies' link relation appearing as a child of an atom:entry element
indicates that the referenced resource MAY contain responses to the
containing atom:entry.
Atom link elements specifying 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" link MAY also contain a "thr:when" attribute whose
value is a [RFC3339] date-time stamp conforming to the same
construction rules as the Date Construct from [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 24, 2006 [Page 7]
Internet-Draft Feed Thread February 2006
For example, replies contained in a separate Atom feed
http://www.example.org/myfeedMy Example Feed2005-07-28T12:00:00ZJamestag:entries.com,2005:1
My original entryThis 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.
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
[RFC4287].
Attribute Value: replies
Description: (see section 4)
Expected display characteristics: (see section 4)
Security considerations: (see section 6)
Snell Expires August 24, 2006 [Page 8]
Internet-Draft Feed Thread February 2006
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
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 August 24, 2006 [Page 9]
Internet-Draft Feed Thread February 2006
Author's Address
James M Snell
Phone:
Email: jasnell@gmail.com
URI: http://snellspace.com
Snell Expires August 24, 2006 [Page 10]
Internet-Draft Feed Thread February 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 August 24, 2006 [Page 11]