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2 Network Working Group J. Snell
3 Internet-Draft A. Sewe
4 Expires: February 18, 2007 August 17, 2006
6 Atom Ranking Extensions
7 draft-snell-atompub-feed-index-10.txt
9 Status of this Memo
11 By submitting this Internet-Draft, each author represents that any
12 applicable patent or other IPR claims of which he or she is aware
13 have been or will be disclosed, and any of which he or she becomes
14 aware will be disclosed, in accordance with Section 6 of BCP 79.
16 Internet-Drafts are working documents of the Internet Engineering
17 Task Force (IETF), its areas, and its working groups. Note that
18 other groups may also distribute working documents as Internet-
19 Drafts.
21 Internet-Drafts are draft documents valid for a maximum of six months
22 and may be updated, replaced, or obsoleted by other documents at any
23 time. It is inappropriate to use Internet-Drafts as reference
24 material or to cite them other than as "work in progress."
26 The list of current Internet-Drafts can be accessed at
27 http://www.ietf.org/ietf/1id-abstracts.txt.
29 The list of Internet-Draft Shadow Directories can be accessed at
30 http://www.ietf.org/shadow.html.
32 This Internet-Draft will expire on February 18, 2007.
34 Copyright Notice
36 Copyright (C) The Internet Society (2006).
38 Abstract
40 This document defines an Atom Syndication Format extension for
41 numerically ranking entries within a syndication feed.
43 Table of Contents
45 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
46 1.1. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 3
47 1.2. Namespace and Version . . . . . . . . . . . . . . . . . . 4
48 1.3. Notational Conventions . . . . . . . . . . . . . . . . . . 4
49 2. The "re:rank" Element . . . . . . . . . . . . . . . . . . . . 5
50 2.1. The "scheme" Attribute . . . . . . . . . . . . . . . . . . 6
51 2.2. The "domain" Attribute . . . . . . . . . . . . . . . . . . 6
52 2.3. The "label" Attribute . . . . . . . . . . . . . . . . . . 6
53 3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
54 4. Security Considerations . . . . . . . . . . . . . . . . . . . 6
55 5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
56 5.1. Normative References . . . . . . . . . . . . . . . . . . . 7
57 5.2. Informative References . . . . . . . . . . . . . . . . . . 7
58 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 8
59 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
60 Intellectual Property and Copyright Statements . . . . . . . . . . 10
62 1. Introduction
64 This document specifies an extension to the Atom Syndication Format
65 that allows feed publishers to convey one or more numeric rankings
66 for entries contained within Atom Feed or Entry Documents, each of
67 which can be used, independently or in conjunction with the others,
68 to establish a sorting order.
70 1.1. Examples
72 For example, the feed below includes two entries representing student
73 exam scores. Each entry contains, in the form of "re:rank" elements,
74 both the overall score for each student and their score for the
75 mathematics portion of the test.
77
79 http://example.org/sat/scores
80 ...
81
82 http://students.example.org/~alice
83 Alice
84 2100
86 750
88 ...
89
90
91 http://students.example.org/~bob
92 Bob
93 2300
95 700
97 ...
98
99
101 Implementations can use the "scheme" attribute associated with each
102 rank to determine how to interpret and validate the numeric value of
103 a "re:rank" element. For instance, a rank value of 700 might have a
104 different meaning and significance when expressed in terms of overall
105 exam scores than it would when expressed in terms of just the
106 mathematics portion of the test.
108 In others situations, rank values that should be interpreted in the
109 same way differ only in terms of the context in which they have been
110 applied. For example, the feed below includes two entries
111 representing movies from two different genres. Each entry contains
112 one popularity ranking relative to all movies regardless of genre,
113 and one ranking that is relative only to other movies in the same
114 genre.
116
118 ...
119
120 http://example.com/movies/starwars
121 Star Wars
122 123
124 53
126 ...
127
128
129 http://example.com/movies/citylights
130 Charlie Chaplin: City Lights
131 5734
133 27
135 ...
136
137
139 1.2. Namespace and Version
141 The XML Namespaces URI [W3C.REC-xml-names-19990114] for the XML
142 elements and attributes described in this specification is
143 http://purl.org/atompub/rank/1.0
145 For convenience, this extension may be referred to as "Feed Rank
146 1.0".
148 1.3. Notational Conventions
150 In this document, the namespace prefix "re:" is used for the above
151 Namespace URI. Note that the choice of namespace prefix is arbitrary
152 and not semantically significant.
154 This extension is, like the Atom Syndication Format [RFC4287] itself,
155 specified using terms from the XML Infoset [W3C.REC-xml-infoset-
156 20040204]. However, this specification uses a shorthand form for two
157 commons terms: The phrase "Information Item" is omitted when naming
158 Element and Attribute Information Items. Therefore, when this
159 specification uses the term "element," it is referring to an Element
160 Information Item in Infoset terms. Likewise, when it uses the term
161 "attribute," it is referring to an Attribute Information Item.
163 Some sections of this specification are illustrated with fragments of
164 a non-normative RELAX NG Compact schema [RFC4287]. In those sections
165 this specification uses the atomCommonAttributes and atomURI patterns
166 defined in [RFC4287]. However, the text of this specification
167 provides the sole definition of conformance.
169 This specification allows the use of IRIs [RFC3987]. Every URI
170 [RFC3986] is also an IRI, so a URI may be used wherever an IRI is
171 named. Note that the definition of "IRI" excludes relative
172 references.
174 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
175 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
176 document are to be interpreted as described in BCP 14, [RFC2119].
178 2. The "re:rank" Element
180 The "re:rank" element conveys a numeric rank associated with an
181 entry.
183 rankingValue = element re:rank {
184 atomCommonAttributes,
185 attribute scheme { atomUri },
186 attribute domain { atomUri }?,
187 attribute label { text }?,
188 { xsd:decimal }
189 }
191 The text content of the element is a decimal value conforming to the
192 lexical representation of the XML Schema decimal data type [W3C.REC-
193 xmlschema-2-20041028]. Whitespace that leads or trails the value is
194 insignificant.
196 Entries MAY contain zero or more "re:rank" elements but MUST NOT
197 contain more than one with the same combination of "scheme" and
198 "domain" attribute values.
200 This specification assigns no significance to the order of "re:rank"
201 elements within an entry.
203 2.1. The "scheme" Attribute
205 Each "re:rank" element MUST have a "scheme" attribute that conveys a
206 permanent, universally unique identifier for a ranking scheme.
208 The content of the attribute MUST be an IRI, as defined by [RFC3987].
209 Though the IRI might use a dereferencable scheme, processors MUST NOT
210 assume it can be dereferenced.
212 Scheme IRIs MUST be compared on a case-sensitive, character-by-
213 character basis. For further information refer to section 4.2.6 of
214 [RFC4287].
216 2.2. The "domain" Attribute
218 Each "re:rank" element MAY have a "domain" attribute that conveys a
219 permanent, universally unique identifier for a ranking domain. If
220 the "domain" atribute is not specified, the domain identifier is
221 either
223 o The "atom:id" of the containing entry's "atom:source" element, if
224 present, or
225 o The "atom:id" of an "atom:feed" containing the entry, if any, or
226 o The value of the ranked entry's "atom:id".
228 The content of the attribute MUST be an IRI, as defined by [RFC3987].
229 Though the IRI might use a dereferencable scheme, processors MUST NOT
230 assume it can be dereferenced.
232 Domain IRIs MUST be compared on a case-sensitive, character-by-
233 character basis. For further information refer to section 4.2.6 of
234 [RFC4287].
236 2.3. The "label" Attribute
238 Each "re:rank" element MAY have a "label" attribute which coneys a
239 Language-Sensitive, human-readable label for the rank. Entities such
240 as "&" and "<" represent their corresponding characters ("&"
241 and "<", respectively), not markup.
243 3. IANA Considerations
245 There are no IANA considerations introduced by this specification.
247 4. Security Considerations
248 The security considerations discussed in section 8 of [RFC4287]
249 apply.
251 Malicious content producers can use illegitimate "r:rank" values to
252 inappropriately boost the positions of their own entries or
253 negatively impact the postions of other entries in ordered sets.
255 5. References
257 5.1. Normative References
259 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
260 Requirement Levels", BCP 14, RFC 2119, March 1997.
262 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
263 Resource Identifier (URI): Generic Syntax", STD 66,
264 RFC 3986, January 2005.
266 [RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource
267 Identifiers (IRIs)", RFC 3987, January 2005.
269 [RFC4287] Nottingham, M., Ed. and R. Sayre, Ed., "The Atom
270 Syndication Format", RFC 4287, December 2005.
272 [W3C.REC-xml-infoset-20040204]
273 Cowan, J. and R. Tobin, "XML Information Set (Second
274 Edition)", World Wide Web Consortium Recommendation
275 http://www.w3.org/TR/2004/REC-xml-infoset-20040204,
276 February 2004.
278 [W3C.REC-xml-names-19990114]
279 Bray, T., Hollander, D., and A. Layman, "Namespaces in
280 XML", World Wide Web Consortium Recommendation http://
281 www.w3.org/TR/1999/REC-xml-names-19990114, January 1999.
283 [W3C.REC-xmlschema-2-20041028]
284 Biron, P. and A. Malhotra, "XML Schema Part 2: Datatypes
285 Second Edition", World Wide Web Consortium Recommendation
286 http://www.w3.org/TR/2004/REC-xmlschema-2-20041028,
287 October 2004.
289 5.2. Informative References
291 [RELAXNG] Clark, J., "RELAX NG Compact Syntax", December 2001,
292 .
295 Appendix A. Acknowledgements
297 The authors gratefully acknowledge the feedback from the Atom
298 Publishing working group during the development of this
299 specification. Some portions of text in this specification have been
300 copied verbatim from [RFC4287] for the purpose of maintaining
301 stylistic and functional consistency with that specification.
303 Authors' Addresses
305 James M Snell
307 Email: jasnell@gmail.com
308 URI: http://www.snellspace.com
310 Andreas Sewe
312 Email: sewe@rbg.informatik.tu-darmstadt.de
313 URI:
315 Intellectual Property Statement
317 The IETF takes no position regarding the validity or scope of any
318 Intellectual Property Rights or other rights that might be claimed to
319 pertain to the implementation or use of the technology described in
320 this document or the extent to which any license under such rights
321 might or might not be available; nor does it represent that it has
322 made any independent effort to identify any such rights. Information
323 on the procedures with respect to rights in RFC documents can be
324 found in BCP 78 and BCP 79.
326 Copies of IPR disclosures made to the IETF Secretariat and any
327 assurances of licenses to be made available, or the result of an
328 attempt made to obtain a general license or permission for the use of
329 such proprietary rights by implementers or users of this
330 specification can be obtained from the IETF on-line IPR repository at
331 http://www.ietf.org/ipr.
333 The IETF invites any interested party to bring to its attention any
334 copyrights, patents or patent applications, or other proprietary
335 rights that may cover technology that may be required to implement
336 this standard. Please address the information to the IETF at
337 ietf-ipr@ietf.org.
339 Disclaimer of Validity
341 This document and the information contained herein are provided on an
342 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
343 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
344 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
345 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
346 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
347 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
349 Copyright Statement
351 Copyright (C) The Internet Society (2006). This document is subject
352 to the rights, licenses and restrictions contained in BCP 78, and
353 except as set forth therein, the authors retain all their rights.
355 Acknowledgment
357 Funding for the RFC Editor function is currently provided by the
358 Internet Society.