From: http://www.ietf.org/internet-drafts/draft-snell-atompub-feed-index-00.txt Title: Feed Index: Enabling Ordered Entries in Atom Reference: IETF Network Working Group, Internet Draft 'draft-snell-atompub-feed-index-00.txt' Date: July 19, 2005 ======================================================================== Network Working Group J. Snell Internet-Draft July 19, 2005 Expires: January 20, 2006 Feed Index: Enabling Ordered Entries in Atom draft-snell-atompub-feed-index-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 20, 2006. Copyright Notice Copyright (C) The Internet Society (2005). Abstract This memo presents a mechanism that allows feed publishers to establish a numeric sorting index for the entries contained within a feed. Snell Expires January 20, 2006 [Page 1] Internet-Draft Feed Index July 2005 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 3 3. The 'i:indexed' Element . . . . . . . . . . . . . . . . . . . 4 4. The 'i:index' Element . . . . . . . . . . . . . . . . . . . . 4 5. Presenting Ordering Entries . . . . . . . . . . . . . . . . . 4 6. Validation . . . . . . . . . . . . . . . . . . . . . . . . . . 6 7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Author's Address . . . . . . . . . . . . . . . . . . . . . . . 8 Intellectual Property and Copyright Statements . . . . . . . . 9 Snell Expires January 20, 2006 [Page 2] Internet-Draft Feed Index July 2005 1. Introduction In syndication document formats such as Atom [I-D.ietf-atompub- format] and RSS ([http://purl.org/rss/1.0/spec][http:// blogs.law.harvard.edu/tech/rss]), the order of entries as presented in the list is typically insignificant. This presents a challenge when the list of entries is intended to represent an ordered list of elements. This document specifies a mechanism that allows feed publishers to specify a numeric index within a feed that may be used to order entries. Although it refers to Atom normatively, the mechanism described herein can be used with similar syndication formats, such as the various flavors of RSS. 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 or similar construct from other syndication formats (e.g., RSS) that are contained within a feed. In this specification, "feed" refers to an Atom Feed Document or similar syndication format (e.g., RSS) that contains a collection of entries. In this specification, "head section" refers to the children of a feed document's document-wide metadata container; e.g., the child elements of the atom:feed element in an Atom Feed Document. In this specification, "index" refers a nonNegativeInteger as defined by section 3.3.20 of [W3C.REC-xmlschema-2-20041028]. 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; "i": "http://purl.org/syndication/index/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. Snell Expires January 20, 2006 [Page 3] Internet-Draft Feed Index July 2005 3. The 'i:indexed' Element The i:indexed element MAY occur no more than once in a feed's head section and indicates that the entries within the feed will have an associated index that may be used to sort the entries. The element's value MUST be empty. For example, The i:indexed element MAY have a sort attribute whose value indicates the default sort order for indexed entries. The attribute's value MUST be either "desc" indicating a descending sort order (highest number first) or "asc" indicating an ascending sort order (lowest number first). If the sort attribute is omitted, a value of "asc" is assumed. The value of the sort attribute is case insensitive. For example, The i:indexed element MUST NOT contain any other attributes. A feed that does not contain an i:indexed element MUST NOT contain any i:index elements. 4. The 'i:index' Element The i:index element conveys a nonNegativeInteger as specified by [W3C.REC-xmlschema-2-20041028] used to order entries within a feed. If the feed's head section contains an i:indexed element, every entry within that feed MUST have a i:index element. The value of each i:index element MUST NOT be used more than once within a feed, ensuring that no two elements ever share the same index value. The index values are not required to be contiguous. The i:indexed element MUST NOT contain any attributes. For example, 1 5. Presenting Ordering Entries When presented with a feed whose head section contains an i:indexed element, a consumer MAY present the entries ordered in either an ascending or descending order based on the value of the i:index element and the value of the i:indexed element's sort attribute if present (ascending order if not). Snell Expires January 20, 2006 [Page 4] Internet-Draft Feed Index July 2005 For example, ... tag:entry:1 3 ... tag:entry:2 2 ... tag:entry:3 1 ... When presented, the entries from the example feed would be sorted in ascending order, or: 1. tag:entry:3 2. tag:entry:2 3. tag:entry:1 While entries within a feed containing an i:indexed element are required to have i:index elements, a consumer MAY still wish to display indexed feeds whose entries do not contain indexes. In this case, entries within an indexed feed that do not contain i:index elements MUST be displayed at the end of the list regardless of sort order. Snell Expires January 20, 2006 [Page 5] Internet-Draft Feed Index July 2005 For example, ... tag:entry:1 3 ... tag:entry:2 2 ... tag:entry:3 1 ... tag:entry:4 ... 1. tag:entry:3 2. tag:entry:2 3. tag:entry:1 4. tag:entry:4 Consumers are not required to present entries in the order established by the i:indexed and i:index elements. 6. Validation It is a validation error if a feed contains an i:indexed element but one or more of it's entries do not contain an i:index element. It is a validation error if two i:index elements within a single feed specify the same nonNegativeInteger value. Snell Expires January 20, 2006 [Page 6] Internet-Draft Feed Index July 2005 It is a validation warning if a one or more feed entries contains an i:index element but the feed head section does not contain an i:indexed element. It is a validation error if the i:indexed element contains any attributes other than sort. It is a validation error if the i:indexed element's sort attribute, if present, specifies any value other than "asc" and "desc". The value is case insensitive. e.g. "asc", "Asc", "ASC", "aSc", etc are all valid variations of "asc". It is a validation error if the i:indexed element's value is not empty. It is a validation error if the i:index element contains any attributes. It is a validation error if the i:index element's value is anything other than a nonNegativeInteger as specified by [W3C.REC-xmlschema-2- 20041028]. 7. Security Considerations It is possible for malicious intermediaries to alter the indexes specified for entries within a feed or to alter the default sort order as specified by the i:indexed element. This risk can be mitigated by digitally signing the indexed feed such the i:indexed and i:index elements are covered by the signatures. 8. 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 20, 2006 [Page 7] Internet-Draft Feed Index July 2005 [W3C.REC-xmlschema-2-20041028] Malhotra, A. and P. Biron, "XML Schema Part 2: Datatypes Second Edition", W3C REC REC-xmlschema-2-20041028, October 2004. Author's Address James M Snell Phone: Email: jasnell@gmail.com URI: http://snellspace.com Snell Expires January 20, 2006 [Page 8] Internet-Draft Feed Index 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. 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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 (2005). 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 January 20, 2006 [Page 9]