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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 2005 4 Expires: February 2, 2006 6 Atom Entry Expiration: Specifying Expiration Timestamps for Atom Entry 7 metadata 8 draft-snell-atompub-feed-expires-03.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 2, 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; 122 {Ed. Note: this namespace MUST be changed to a proper IETF namespace 123 scheme prior to publication} 124 "age": "http://purl.org/atompub/age/1.0" 126 This specification uses terms from the XML Infoset [W3C.REC-xml- 127 infoset-20040204]. However, this specification uses a shorthand; the 128 phrase "Information Item" is omitted when naming Element Information 129 Items. Therefore, when this specification uses the term "element," 130 it is referring to an Element Information Item in Infoset terms. 132 This specification defines the notion of a Non-Negative Integer 133 Construct whose value MUST conform to the canonical representation of 134 the "nonNegativeInteger" construction defined by [W3C.REC-xmlschema- 135 2-20041028]. The value of the Non-Negative Integer Construct MUST 136 NOT contain any leading or trailing whitespace. 137 nonNegativeIntegerConstruct = 138 atomCommonAttributes, 139 xsd:nonNegativeInteger 141 Example Non-Negative Integer Constructs 142 0 143 1000000 145 3. The 'expires' extension element 147 The 'expires' extension element conforms to the Atom Date Construct 148 and is used to indicate a precise moment in time (inclusive) when the 149 information content of an entry expires. 150 expiresElement = element age:expires { atomDateConstruct } 152 o atom:entry elements MAY contain exactly one 'expires' extension 153 element. 155 o atom:feed elements MAY contain exactly one 'expires' extension 156 element. 157 o atom:source elements MAY contain exactly one 'expires' extension 158 element. 159 o An atom:entry that contains an 'expires' extension element MUST 160 NOT contain a 'max-age' extension element. 161 o An atom:feed that contains an 'expires' extension element MUST NOT 162 contain a 'max-age' extension element. 163 o An atom:source that contains an 'expires' extension element MUST 164 NOT contain a 'max-age' extension element. 166 For example 167 169 http://www.example.com/myfeed 170 My Example Feed 171 2005-07-28T12:00:00Z 172 173 James 174 175 tag:entries.com,2005:1 176 An entry with an expiration timestamp 177 178 2005-12-12T12:00:00Z 179 An entry with an expiration 180 181 183 4. The 'max-age' extension element 185 The 'max-age' extension element is used to indicate the maximum age 186 of the information content in miliseconds from the moment specified 187 by the atom:updated element. The value is specified as a non- 188 negative integer conforming to the nonNegativeIntegerConstruct. 189 maxAgeElement = element age:max-age { nonNegativeIntegerConstruct } 191 o atom:entry elements MAY contain exactly one 'max-age' extension 192 element. 193 o atom:feed elements MAY contain exactly one 'max-age' extension 194 element. 195 o atom:source elements MAY contain exactly one 'max-age' extension 196 element. 197 o An atom:entry that contains a 'max-age' extension element MUST NOT 198 contain an 'expires' extension element. 199 o An atom:feed that contains a 'max-age' extension element MUST NOT 200 contain an 'expires' extension element. 202 o An atom:source that contains a 'max-age' extension element MUST 203 NOT contain an 'expires' extension element. 205 For example 206 208 http://www.example.com/myfeed 209 My Example Feed 210 2005-07-28T12:00:00Z 211 212 James 213 214 tag:entries.com,2005:1 215 An entry with a maximum age of 20 seconds 216 217 20000 218 expire after a mere 20 seconds 219 220 222 5. Security Considerations 224 It is possible for malicious intermediaries to alter the expiration 225 metadata in an Atom document. This risk can be mitigated by 226 digitally signing the elements in which the 'expires' or 'max-age' 227 extension elements appear. It is strongly recommended that 228 implementations discard expired information content or otherwise warn 229 users that the information content has expired. 231 6. IANA Considerations 233 There are no IANA considerations introduced by this specification. 235 7. References 237 [I-D.ietf-atompub-format] 238 Sayre, R. and M. Nottingham, "The Atom Syndication 239 Format", draft-ietf-atompub-format-11 (work in progress), 240 August 2005. 242 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 243 Requirement Levels", BCP 14, RFC 2119, March 1997. 245 [W3C.REC-xml-infoset-20040204] 246 Tobin, R. and J. Cowan, "XML Information Set (Second 247 Edition)", W3C REC REC-xml-infoset-20040204, 248 February 2004. 250 [W3C.REC-xml-names-19990114] 251 Hollander, D., Bray, T., and A. Layman, "Namespaces in 252 XML", W3C REC REC-xml-names-19990114, January 1999. 254 [W3C.REC-xmlschema-2-20041028] 255 Malhotra, A. and P. Biron, "XML Schema Part 2: Datatypes 256 Second Edition", W3C REC REC-xmlschema-2-20041028, 257 October 2004. 259 Author's Address 261 James M Snell 263 Phone: 264 Email: jasnell@gmail.com 265 URI: http://snellspace.com 267 Appendix A. Acknowledgements 269 The author gratefully acknowledges the feedback from Eric Scheid, 270 Walter Underwood, Henry Story and the other members of Atom 271 Publishing Format and Protocol working group during the development 272 of this specification. 274 Intellectual Property Statement 276 The IETF takes no position regarding the validity or scope of any 277 Intellectual Property Rights or other rights that might be claimed to 278 pertain to the implementation or use of the technology described in 279 this document or the extent to which any license under such rights 280 might or might not be available; nor does it represent that it has 281 made any independent effort to identify any such rights. 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