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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 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. 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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 301 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 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.