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--------------------------------------------------------------------------------
2 Network Working Group J. Snell
3 Internet-Draft August 22, 2005
4 Expires: February 23, 2006
6 Atom Entry Expiration: Specifying Expiration Timestamps for Atom Entry
7 metadata
8 draft-snell-atompub-feed-expires-01.txt
10 Status of this Memo
12 By submitting this Internet-Draft, each author represents that any
13 applicable patent or other IPR claims of which he or she is aware
14 have been or will be disclosed, and any of which he or she becomes
15 aware will be disclosed, in accordance with Section 6 of BCP 79.
17 Internet-Drafts are working documents of the Internet Engineering
18 Task Force (IETF), its areas, and its working groups. Note that
19 other groups may also distribute working documents as Internet-
20 Drafts.
22 Internet-Drafts are draft documents valid for a maximum of six months
23 and may be updated, replaced, or obsoleted by other documents at any
24 time. It is inappropriate to use Internet-Drafts as reference
25 material or to cite them other than as "work in progress."
27 The list of current Internet-Drafts can be accessed at
28 http://www.ietf.org/ietf/1id-abstracts.txt.
30 The list of Internet-Draft Shadow Directories can be accessed at
31 http://www.ietf.org/shadow.html.
33 This Internet-Draft will expire on February 23, 2006.
35 Copyright Notice
37 Copyright (C) The Internet Society (2005).
39 Abstract
41 This memo presents a mechanism that allows feed publishers to express
42 maximum age and expiration properties for information content within
43 an Atom entry.
45 Table of Contents
47 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
48 2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 3
49 3. The 'expires' extension element . . . . . . . . . . . . . . . 4
50 4. The 'max-age' extension element . . . . . . . . . . . . . . . 5
51 5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
52 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
53 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
54 Author's Address . . . . . . . . . . . . . . . . . . . . . . . 7
55 A. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
56 Intellectual Property and Copyright Statements . . . . . . . . 8
58 1. Introduction
60 This document specifies a mechanism that allows the expression of
61 expiration timestamps and maximum age properties for information
62 content within the Atom Syndication Format ([I-D.ietf-atompub-
63 format]). The mechanism defines two mutually exclusive extension
64 elements that may be used to specify either an exact instant that the
65 information content of an atom:entry expires, or a maximum age from
66 the moment specified by an entries atom:updated element.
68 When an atom:feed, atom:entry or atom:source contains an 'expires' or
69 'max-age' extension element, the information content of the contained
70 element is considered to be 'time constrained'. Time constrainted
71 information content is considered to be either 'active' or 'expired'.
72 The default state is 'active'. When the age (calculated in
73 miliseconds from the moment specified by the atom:updated element)
74 exceeds the value specified by the 'max-age' extension, or when the
75 moment specified by the 'expires' extension elements passes, the
76 state of the time constrained information content MUST be considered
77 to be 'expired' and no longer valid. It is strongly recommended that
78 implementations either discard 'expired' information content or
79 otherwise warn users that the information content has expired.
81 The mechanism defined herein MUST NOT be used to support the caching
82 of Atom documents and MUST NOT be used to schedule when a client
83 should revisit/refresh local copies of Atom documents. Specifically,
84 the 'expires' and 'max-age' extension elements are relevant only to
85 the informational content within an atom:entry and are not relevant
86 to the Atom Feed and Entry Documents in which they happen to appear.
88 The presence of an 'expires' or 'max-age' extension within an atom:
89 feed element is relevant only to the informational content of the
90 containing element and not to any contained atom:entry elements.
91 Likewise, the presence of an 'expires' or 'max-age' extension within
92 an atom:source element is relevant only to the informational content
93 of the containing atom:source element and not to the atom:entry that
94 contains the atom:source.
96 2. Notational Conventions
98 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
99 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
100 document are to be interpreted as described in BCP 14, [RFC2119], as
101 scoped to those conformance targets.
103 In this specification, "entry" refers to an atom:entry element.
105 In this specification, "feed" refers to an Atom Feed Document.
107 In this specification, "head section" refers to the children of a
108 feed's document-wide metadata container; e.g., the child elements of
109 the atom:feed element in an Atom Feed Document.
111 In this specification, the term "extension element" refers to a
112 structured extension element as described in [I-D.ietf-atompub-
113 format].
115 In this specification, the term "information content" refers to the
116 collection of metadata relevant to an atom:entry element.
118 This specification uses XML Namespaces [W3C.REC-xml-names-19990114]
119 to uniquely identify XML element names. It uses the following
120 namespace prefix for the indicated namespace URI;
121 "age": "http://purl.org/syndication/age/1.0"
123 This specification uses terms from the XML Infoset [W3C.REC-xml-
124 infoset-20040204]. However, this specification uses a shorthand; the
125 phrase "Information Item" is omitted when naming Element Information
126 Items. Therefore, when this specification uses the term "element,"
127 it is referring to an Element Information Item in Infoset terms.
129 This specification defines the notion of a Non-Negative Integer
130 Construct whose value MUST conform to the canonical representation of
131 the "nonNegativeInteger" construction defined by [W3C.REC-xmlschema-
132 2-20041028]. The value of the Non-Negative Integer Construct MUST
133 NOT contain any leading or trailing whitespace.
134 nonNegativeIntegerConstruct =
135 atomCommonAttributes,
136 xsd:nonNegativeInteger
138 Example Non-Negative Integer Constructs
139 0
140 1000000
142 3. The 'expires' extension element
144 The 'expires' extension element conforms to the Atom Date Construct
145 and is used to indicate a precise moment in time (inclusive) when the
146 information content of an entry expires.
147 expiresElement = element age:expires { atomDateConstruct }
149 o atom:entry elements MAY contain exactly one 'expires' extension
150 element.
151 o atom:feed elements MAY contain exactly one 'expires' extension
152 element.
154 o atom:source elements MAY contain exactly one 'expires' extension
155 element.
156 o An atom:entry that contains an 'expires' extension element MUST
157 NOT contain a 'max-age' extension element.
158 o An atom:feed that contains an 'expires' extension element MUST NOT
159 contain a 'max-age' extension element.
160 o An atom:source that contains an 'expires' extension element MUST
161 NOT contain a 'max-age' extension element.
163 For example
164
166 http://www.example.com/myfeed
167 My Example Feed
168 2005-07-28T12:00:00Z
169
170 James
171
172 tag:entries.com,2005:1
173 An entry with an expiration timestamp
174
175 2005-12-12T12:00:00Z
176 An entry with an expiration
177
178
180 4. The 'max-age' extension element
182 The 'max-age' extension element is used to indicate the maximum age
183 of the information content in miliseconds from the moment specified
184 by the atom:updated element. The value is specified as a non-
185 negative integer conforming to the nonNegativeIntegerConstruct.
186 maxAgeElement = element age:max-age { nonNegativeIntegerConstruct }
188 o atom:entry elements MAY contain exactly one 'max-age' extension
189 element.
190 o atom:feed elements MAY contain exactly one 'max-age' extension
191 element.
192 o atom:source elements MAY contain exactly one 'max-age' extension
193 element.
194 o An atom:entry that contains a 'max-age' extension element MUST NOT
195 contain an 'expires' extension element.
196 o An atom:feed that contains a 'max-age' extension element MUST NOT
197 contain an 'expires' extension element.
198 o An atom:source that contains a 'max-age' extension element MUST
199 NOT contain an 'expires' extension element.
201 For example
202
204 http://www.example.com/myfeed
205 My Example Feed
206 2005-07-28T12:00:00Z
207
208 James
209
210 tag:entries.com,2005:1
211 An entry with a maximum age of 20 seconds
212
213 20000
214 expire after a mere 20 seconds
215
216
218 5. Security Considerations
220 It is possible for malicious intermediaries to alter the expiration
221 metadata in an Atom document. This risk can be mitigated by
222 digitally signing the elements in which the 'expires' or 'max-age'
223 extension elements appear. It is strongly recommended that
224 implementations discard expired information content or otherwise warn
225 users that the information content has expired.
227 6. IANA Considerations
229 There are no IANA considerations introduced by this specification.
231 7. References
233 [I-D.ietf-atompub-format]
234 Sayre, R. and M. Nottingham, "The Atom Syndication
235 Format", draft-ietf-atompub-format-11 (work in progress),
236 August 2005.
238 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
239 Requirement Levels", BCP 14, RFC 2119, March 1997.
241 [W3C.REC-xml-infoset-20040204]
242 Tobin, R. and J. Cowan, "XML Information Set (Second
243 Edition)", W3C REC REC-xml-infoset-20040204,
244 February 2004.
246 [W3C.REC-xml-names-19990114]
247 Hollander, D., Bray, T., and A. Layman, "Namespaces in
248 XML", W3C REC REC-xml-names-19990114, January 1999.
250 [W3C.REC-xmlschema-2-20041028]
251 Malhotra, A. and P. Biron, "XML Schema Part 2: Datatypes
252 Second Edition", W3C REC REC-xmlschema-2-20041028,
253 October 2004.
255 Author's Address
257 James M Snell
259 Phone:
260 Email: jasnell@gmail.com
261 URI: http://snellspace.com
263 Appendix A. Acknowledgements
265 The author gratefully acknowledges the feedback from Eric Scheid,
266 Walter Underwood, Henry Story and the other members of Atom
267 Publishing Format and Protocol working group during the development
268 of this specification.
270 Intellectual Property Statement
272 The IETF takes no position regarding the validity or scope of any
273 Intellectual Property Rights or other rights that might be claimed to
274 pertain to the implementation or use of the technology described in
275 this document or the extent to which any license under such rights
276 might or might not be available; nor does it represent that it has
277 made any independent effort to identify any such rights. Information
278 on the procedures with respect to rights in RFC documents can be
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281 Copies of IPR disclosures made to the IETF Secretariat and any
282 assurances of licenses to be made available, or the result of an
283 attempt made to obtain a general license or permission for the use of
284 such proprietary rights by implementers or users of this
285 specification can be obtained from the IETF on-line IPR repository at
286 http://www.ietf.org/ipr.
288 The IETF invites any interested party to bring to its attention any
289 copyrights, patents or patent applications, or other proprietary
290 rights that may cover technology that may be required to implement
291 this standard. Please address the information to the IETF at
292 ietf-ipr@ietf.org.
294 Disclaimer of Validity
296 This document and the information contained herein are provided on an
297 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
298 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
299 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
300 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
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302 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
304 Copyright Statement
306 Copyright (C) The Internet Society (2005). This document is subject
307 to the rights, licenses and restrictions contained in BCP 78, and
308 except as set forth therein, the authors retain all their rights.
310 Acknowledgment
312 Funding for the RFC Editor function is currently provided by the
313 Internet Society.