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'2' Summary: 10 errors (**), 0 flaws (~~), 2 warnings (==), 11 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group M. Nottingham, Ed. 3 Internet-Draft September 5, 2004 4 Expires: March 6, 2005 6 The Atom Syndication Format 7 draft-ietf-atompub-format-02 9 Status of this Memo 11 By submitting this Internet-Draft, I certify that any applicable 12 patent or other IPR claims of which I am aware have been disclosed, 13 and any of which I become aware will be disclosed, in accordance with 14 RFC 3668. 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 19 Internet-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 March 6, 2005. 34 Copyright Notice 36 Copyright (C) The Internet Society (2004). All Rights Reserved. 38 Abstract 40 This document specifies Atom, an XML-based Web content and metadata 41 syndication format. 43 Table of Contents 45 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 46 1.1 Editorial Notes . . . . . . . . . . . . . . . . . . . . . 4 47 1.2 Example . . . . . . . . . . . . . . . . . . . . . . . . . 5 48 1.3 Conformance . . . . . . . . . . . . . . . . . . . . . . . 5 49 1.4 Notational Conventions . . . . . . . . . . . . . . . . . . 5 50 2. Atom Documents . . . . . . . . . . . . . . . . . . . . . . . 7 51 3. Common Atom Constructs . . . . . . . . . . . . . . . . . . . 9 52 3.1 Content Constructs . . . . . . . . . . . . . . . . . . . . 9 53 3.1.1 "type" Attribute . . . . . . . . . . . . . . . . . . . 9 54 3.1.2 "mode" Attribute . . . . . . . . . . . . . . . . . . . 9 55 3.2 Person Constructs . . . . . . . . . . . . . . . . . . . . 9 56 3.2.1 "atom:name" Element . . . . . . . . . . . . . . . . . 10 57 3.2.2 "atom:uri" Element . . . . . . . . . . . . . . . . . . 10 58 3.2.3 "atom:email" Element . . . . . . . . . . . . . . . . . 10 59 3.3 Date Constructs . . . . . . . . . . . . . . . . . . . . . 10 60 3.4 Link Constructs . . . . . . . . . . . . . . . . . . . . . 10 61 3.4.1 "rel" Attribute . . . . . . . . . . . . . . . . . . . 10 62 3.4.2 "type" Attribute . . . . . . . . . . . . . . . . . . . 11 63 3.4.3 "href" Attribute . . . . . . . . . . . . . . . . . . . 11 64 3.4.4 "hreflang" Attribute . . . . . . . . . . . . . . . . . 11 65 3.4.5 "title" Attribute . . . . . . . . . . . . . . . . . . 11 66 3.5 Identity Constructs . . . . . . . . . . . . . . . . . . . 11 67 3.5.1 Dereferencing Identity Constructs . . . . . . . . . . 11 68 3.5.2 Comparing Identity Constructs . . . . . . . . . . . . 12 69 4. The "atom:feed" Element . . . . . . . . . . . . . . . . . . 13 70 4.1 "version" Attribute . . . . . . . . . . . . . . . . . . . 13 71 4.2 The "atom:head" Element . . . . . . . . . . . . . . . . . 13 72 4.2.1 "atom:title" Element . . . . . . . . . . . . . . . . . 13 73 4.2.2 "atom:link" Element . . . . . . . . . . . . . . . . . 13 74 4.2.3 "atom:author" Element . . . . . . . . . . . . . . . . 14 75 4.2.4 "atom:contributor" Element . . . . . . . . . . . . . . 14 76 4.2.5 "atom:tagline" Element . . . . . . . . . . . . . . . . 14 77 4.2.6 "atom:id" Element . . . . . . . . . . . . . . . . . . 14 78 4.2.7 "atom:generator" Element . . . . . . . . . . . . . . . 14 79 4.2.8 "atom:copyright" Element . . . . . . . . . . . . . . . 15 80 4.2.9 "atom:info" Element . . . . . . . . . . . . . . . . . 15 81 4.2.10 "atom:modified" Element . . . . . . . . . . . . . . 15 82 5. The "atom:entry" Element . . . . . . . . . . . . . . . . . . 16 83 5.1 "atom:title" Element . . . . . . . . . . . . . . . . . . . 16 84 5.2 "atom:link" Element . . . . . . . . . . . . . . . . . . . 16 85 5.3 "atom:author" Element . . . . . . . . . . . . . . . . . . 16 86 5.4 "atom:contributor" Element . . . . . . . . . . . . . . . . 17 87 5.5 "atom:id" Element . . . . . . . . . . . . . . . . . . . . 17 88 5.6 "atom:updated" Element . . . . . . . . . . . . . . . . . . 17 89 5.7 "atom:summary" Element . . . . . . . . . . . . . . . . . . 17 90 5.8 "atom:content" Element . . . . . . . . . . . . . . . . . . 17 91 5.9 "atom:copyright" Element . . . . . . . . . . . . . . . . . 18 92 5.10 "atom:origin" Element . . . . . . . . . . . . . . . . . 18 93 6. Managing Feed State . . . . . . . . . . . . . . . . . . . . 19 94 7. Securing Atom Documents . . . . . . . . . . . . . . . . . . 20 95 7.1 Digital Signatures . . . . . . . . . . . . . . . . . . . . 20 96 7.2 Encryption . . . . . . . . . . . . . . . . . . . . . . . . 20 97 8. Embedding Atom in Other Formats . . . . . . . . . . . . . . 21 98 9. Extending Atom . . . . . . . . . . . . . . . . . . . . . . . 22 99 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . 23 100 11. Security Considerations . . . . . . . . . . . . . . . . . . 24 101 12. Normative References . . . . . . . . . . . . . . . . . . . . 24 102 Author's Address . . . . . . . . . . . . . . . . . . . . . . 25 103 A. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 26 104 B. Revision History . . . . . . . . . . . . . . . . . . . . . . 27 105 Intellectual Property and Copyright Statements . . . . . . . 29 107 1. Introduction 109 Atom is an XML-based document format intended to allow lists of 110 related information, known as "feeds", to be synchronised between 111 publishers and consumers. Feeds are composed of a number of items, 112 known as "entries", each with an extensible set of attached metadata. 113 For example, each entry has a title. 115 The primary use case that Atom addresses is the syndication of Web 116 content such as Weblogs and news headlines to Web sites as well as 117 directly to user agents. However, nothing precludes it from being 118 used for other purposes and kinds of content. 120 Details of comunication protocols between software agents using Atom 121 can be found in the Atom Protocol specification [Atom-protocol]. 123 [[ more motivation / design principles ]] 125 1.1 Editorial Notes 127 The Atom format is a work-in-progress, and this draft is both 128 incomplete and likely to change rapidly. As a result, THE FORMAT 129 DESCRIBED BY THIS DRAFT SHOULD NOT BE DEPLOYED, either in production 130 systems or in any non-experimental fashion on the Internet. 132 Discussion of this draft happens in two fora; 134 The mailing list [1] 135 The Atom Wiki Web site [2] 137 Active development takes place on the mailing list, while the Wiki is 138 used for issue tracking and new proposals. 140 This document is an early draft and known to be incomplete. Topics 141 marked [[like this]] indicate where additional text is likely to be 142 added. 144 1.2 Example 146 A minimal, single-entry Atom Feed Document: 148 149 151 152 Example Feed 153 155 2003-12-13T18:30:02Z 156 157 John Doe 158 159 160 161 Atom-Powered Robots Run Amok 162 164 tag:example.org,2003:3.2397 165 2003-12-13T08:29:29-04:00 166 2003-12-13T18:30:02Z 167 168 170 1.3 Conformance 172 [[ talk about atom documents and atom consumers, and how requirements 173 are placed on them ]] 175 1.4 Notational Conventions 177 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 178 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 179 document are to be interpreted as described in BCP 14, [RFC2119]. 181 This specification uses XML Namespaces [W3C.REC-xml-names-19990114] 182 to uniquely identify XML elements and attribute names. It uses the 183 following namespace prefixes for the indicated namespace URIs; 185 "atom": http://purl.org/atom/ns#draft-ietf-atompub-format-02 187 Note that the choice of any namespace prefix is arbitrary and not 188 semantically significant. 190 Atom is specified using terms from the XML Infoset 192 [W3C.REC-xml-infoset-20011024]. However, this specification uses a 193 shorthand for two common terms; the phrase "Information Item" is 194 omitted when naming Element Information Items and Attribute 195 Information Items. 197 Therefore, when this specification uses the term "element," it is 198 refering to an Element Information Item in Infoset terms. Likewise, 199 when it uses the term "attribute," it is refering to an Attribute 200 Information Item. 202 2. Atom Documents 204 This specification describes two kinds of Atom Documents; Atom Feed 205 Documents and Atom Entry Documents. 207 An Atom Feed Document is a representation of an Atom feed, including 208 metadata about the feed, and some or all of the entries associated 209 with it. Its document element is atom:feed. 211 An Atom Entry Document represents exactly one Atom Entry, outside of 212 the context of an Atom Feed. Its document element is atom:entry. 214 Both kinds of Atom documents are specified in terms of the XML 215 Information Set, serialised as XML 1.0 [W3C.REC-xml-20040204] and 216 identified with the "application/atom+xml" media type. Atom 217 Documents MUST be well-formed XML. 219 [[ Validity? ]] 221 Atom constrains the appearance and content of elements and 222 attributes; unless otherwise stated, Atom Documents MAY contain other 223 Information Items as appropriate. In particular, Comment Information 224 Items and Processing Instruction Information Items SHOULD be ignored 225 in the normal processing of an Atom Document. 227 Any element in an Atom Document MAY have an xml:base attribute. XML 228 Base [W3C.REC-xmlbase-20010627] processing MUST be applied to any 229 relative URI reference present in an Atom document. This includes 230 such elements and attributes as specified by Atom itself, as well as 231 those specified by extensions to Atom. 233 Any element in an Atom Document MAY have an xml:lang attribute, whose 234 content indicates the default natural language of the element's 235 content. Requirements regarding the content and interpretation of 236 xml:lang are specified in XML 1.0 [W3C.REC-xml-20040204] Section 237 2.12. For convenience, the most important are summarised here: 239 o The content of this attribute must be a language tag [RFC3066] or 240 an empty string (e.g., xml:lang=""), which indicates that there is 241 no language information available. 242 o If an element does not have an xml:lang element, the first 243 xml:lang attribute in its ancestors indicates the natural language 244 of its content. 246 [[ feedback as to whether this listing is helpful or not would be 247 appreciated; re-stating the requirements of other specifications is 248 tricky. ]] 250 [[ discussion of URI escaping and i18n ]] 252 [[ discussion of white space ]] 254 Atom is extensible. See the section titled 'Extending Atom' later in 255 this document for a full description of how Atom Documents can be 256 extended. 258 3. Common Atom Constructs 260 Many of Atom's elements share a few common structures. This section 261 defines a few such structures and their requirements, for convenient 262 reference by the appropriate element definitions. 264 When an element is identified as being a particular kind of 265 construct, it inherits the corresponding requirements from that 266 construct's definition in this section. 268 3.1 Content Constructs 270 A Content construct is an element with arbitrary child content, whose 271 properties are described by the following attributes: 273 3.1.1 "type" Attribute 275 Content constructs MAY have a "type" attribute, whose value indicates 276 the media type of the content. When present, this attribute's value 277 MUST be a media type [RFC2045]. If this attribute is not present, 278 processors MUST behave as if it were present with a value of "text/ 279 plain". 281 3.1.2 "mode" Attribute 283 Content constructs MAY have a "mode" attribute, whose value indicates 284 the method used to encode the content. When present, this 285 attribute's value MUST be listed below. If not present, processors 286 MUST behave as if its value were "xml". 288 "xml": A mode attribute with the value "xml" indicates that the 289 element's content is inline xml (for example, namespace-qualified 290 XHTML). 291 "escaped": A mode attribute with the value "escaped" indicates that 292 the element's content is escaped, as defined in 293 [W3C.REC-xml-20040204] (section 4.6). Processors MUST unescape 294 the element's content before considering it as content of the 295 indicated media type. 296 "base64": A mode attribute with the value "base64" indicates that 297 the element's content is base64-encoded [RFC2045]. Processors 298 MUST decode the element's content before considering it as content 299 of the the indicated media type. 301 3.2 Person Constructs 303 A Person construct is an element that describes a person, 304 corporation, or similar entity. 306 Person constructs MAY be extended by namespace-qualified element 307 children. 309 Ordering of the element children of Person constructs MUST NOT be 310 considered significant. 312 3.2.1 "atom:name" Element 314 The "atom:name" element's content conveys a human-readable name for 315 the person. Person constructs MUST contain exactly one "atom:name" 316 element. 318 3.2.2 "atom:uri" Element 320 The "atom:uri" element's content conveys a URI associated with the 321 person. Person constructs MAY contain an atom:uri element, but MUST 322 NOT contain more than one. The content of atom:uri in a Person 323 construct MUST be a URI [RFC2396]. 325 xml:base [W3C.REC-xmlbase-20010627] processing MUST be applied to the 326 atom:uri element's content. 328 3.2.3 "atom:email" Element 330 The "atom:email" element's content conveys an e-mail address 331 associated with the persons. Person constructs MAY contain an 332 atom:email element, but MUST NOT contain more than one. Its content 333 MUST be an e-mail address [RFC2822]. 335 3.3 Date Constructs 337 A Date construct is an element whose content MUST conform to the 338 date-time BNF rule in [RFC3339]. 340 3.4 Link Constructs 342 A Link construct is an element that MUST NOT have any child content, 343 and has the following attributes: 345 3.4.1 "rel" Attribute 347 The "rel" attribute indicates the type of relationship that the link 348 represents. Link constructs MUST have a rel attribute, whose value 349 MUST be one of the values enumerated in the Atom Protocol 350 specification [Atom-protocol]. 352 3.4.2 "type" Attribute 354 The "type" attribute indicates an advisory media type; it MAY be used 355 as a hint to determine the type of the representation which should be 356 returned when the URI in the href attribute is dereferenced. Note 357 that the type attribute does not override the actual media type 358 returned with the representation. 360 Link constructs MUST have a type attribute, whose value MUST be a 361 media type [RFC2045]. 363 3.4.3 "href" Attribute 365 The "href" attribute contains the link's URI. Link constructs MUST 366 have a href attribute, whose value MUST be a URI [RFC2396]. 368 xml:base [W3C.REC-xmlbase-20010627] processing MUST be applied to the 369 href attribute's content. 371 3.4.4 "hreflang" Attribute 373 The "hreflang" attribute's content describes the language of the 374 resource pointed to by the href attribute. When used together with 375 the rel="alternate", it implies a translated version of the entry. 376 Link constructs MAY have an hreflang attribute, whose value MUST be a 377 language tag [RFC3066]. 379 3.4.5 "title" Attribute 381 The "title" attribute conveys human-readable information about the 382 link. Link constructs MAY have a title attribute. 384 3.5 Identity Constructs 386 An Identity construct is an element whose content conveys a 387 permanent, universally unique identifier for the construct's parent. 389 Its content MUST be an absolute URI [RFC2396] that is universally 390 unique; i.e., it MUST NOT change over time, even if the parent feed 391 or entry element is relocated, migrated, syndicated, republished, 392 exported or imported. 394 3.5.1 Dereferencing Identity Constructs 396 The content of an Identity construct MAY be dereferencable (e.g. a 397 HTTP URI). However, processors MUST NOT assume it to be 398 dereferencable. 400 If the identified resource is served dynamically, the content of an 401 Identity construct MUST be created only once and then stored along 402 with the resource. The content of an Identity construct MUST NOT be 403 created dynamically. 405 Because of the risk of confusion between URIs that would be 406 equivalent if dereferenced, the following normalization strategy is 407 strongly encouraged when generating Identity constructs: 409 o Provide the scheme in lowercase characters. 410 o Provide the host, if any, in lowercase characters. 411 o Only perform percent-encoding where it is essential. 412 o Use uppercase A-through-F characters when percent-encoding. 413 o Prevent dot-segments appearing in paths. 414 o For schemes that define a default authority, use an empty 415 authority if the default is desired. 416 o For schemes that define an empty path to be equivalent to a path 417 of "/", use "/". 418 o For schemes that define a port, use an empty port if the default 419 is desired. 420 o Preserve empty fragment identifiers and queries. 421 o Ensure that all portions of the URI are utf-8 encoded NFC form 422 Unicode strings. 424 3.5.2 Comparing Identity Constructs 426 Instances of Identity constructs can be compared to determine whether 427 a entry or feed is the same as one seen before. Processors MUST 428 compare Identity constructs on a character-by-character basis in a 429 case-sensitive fashion. 431 As a result, two URIs that resolve to the same resource but are not 432 character-for-character identical will be considered different for 433 the purposes of Identifier comparison. 435 For example, "http://www.example.org/thing", 436 "http://www.example.org/Thing", "http://www.EXAMPLE.org/thing" and 437 "HTTP://www.example.org/thing" will all be considered different 438 identifiers, despite their differences in case. 440 Likewise, "http://www.example.com/~bob", 441 "http://www.example.com/%7ebob" and "http://www.example.com/%7Ebob" 442 will all be considered different identifiers, because URI %-escaping 443 is significant for the purposes of comparison. 445 XML character and entity references MUST be converted into characters 446 before comparison. 448 4. The "atom:feed" Element 450 The "atom:feed" element is the document (i.e., top-level) element of 451 an Atom Feed Document, acting as a container for metadata and data 452 associated with the feed. Its first element child MUST be atom:head, 453 which MAY be followed zero or more atom:entry child elements. 455 4.1 "version" Attribute 457 atom:feed elements MUST have a "version" attribute whose content 458 indicates the version of the Atom specification that the feed 459 conforms to. The content of this attribute is unstructured text. 461 The version identifier for this specification is 462 "draft-ietf-atompub-format-02: do not deploy". 464 4.2 The "atom:head" Element 466 The atom:head element acts as a container for metadata about the feed 467 itself. 469 The atom:head element MAY contain any namespace-qualified 470 [W3C.REC-xml-names-19990114] elements as children. Ordering of the 471 element children of atom:head element MUST NOT be considered 472 significant. 474 The following child elements are defined by this specification (note 475 that the presence of some of these elements is required): 477 4.2.1 "atom:title" Element 479 The "atom:title" element is a Content construct that conveys a 480 human-readable title for the feed. atom:head elements MUST contain 481 exactly one atom:title element. 483 4.2.2 "atom:link" Element 485 The "atom:link" element is a Link construct that conveys a URI 486 associated with the feed. The nature of the relationship is 487 determined by the construct's rel attribute. 489 atom:head elements MUST contain at least one atom:link element with a 490 rel attribute value of "alternate". 492 atom:head elements MUST NOT contain more than one atom:link element 493 with a rel attribute value of "alternate" that has the same type 494 attribute value. 496 If a feed's atom:link element with type="alternate" resolves to an 497 HTML document, then that document SHOULD have a autodiscovery link 498 element [Atom-autodiscovery] that reflects back to the feed. 500 atom:head elements MAY contain additional atom:link elements beyond 501 those described above. 503 4.2.3 "atom:author" Element 505 The "atom:author" element is a Person construct that indicates the 506 default author of the feed. atom:head elements MUST contain exactly 507 one atom:author element, UNLESS all of the atom:feed element's child 508 atom:entry elements contain an atom:author element. atom:head 509 elements MUST NOT contain more than one atom:author element. 511 [[explain inheritence]] 513 4.2.4 "atom:contributor" Element 515 The "atom:contributor" element is a Person construct that indicates a 516 person or other entity who contributes to the feed. atom:head 517 elements MAY contain one or more atom:contributor elements. 519 4.2.5 "atom:tagline" Element 521 The "atom:tagline" element is a Content construct that conveys a 522 human-readable description or tagline for the feed. atom:head 523 elements MAY contain an atom:tagline element, but MUST NOT contain 524 more than one. 526 4.2.6 "atom:id" Element 528 The "atom:id" element is an Identity construct that conveys a 529 permanent, universally unique identifier for a feed. atom:head 530 elements MAY contain an atom:id element, but MUST NOT contain more 531 than one. 533 4.2.7 "atom:generator" Element 535 The "atom:generator" element's content indentifies the software agent 536 used to generate the feed, for debugging and other purposes. 537 atom:head elements MAY contain an atom:generator element, but MUST 538 NOT contain more than one. 540 The content of this element, when present, MUST be a string that is a 541 human-readable name for the generating agent. 543 The atom:generator element MAY have a "uri" attribute whose value 544 MUST be a URI. When dereferenced, that URI SHOULD produce a 545 representation that is relevant to that agent. 547 The atom:generator element MAY have a "version" attribute that 548 indicates the version of the generating agent. When present, its 549 value is unstructured text. 551 4.2.8 "atom:copyright" Element 553 The "atom:copyright" element is Content construct that conveys a 554 human-readable copyright statement for the feed. atom:head elements 555 MAY contain an atom:copyright element, but MUST NOT contain more than 556 one. 558 The atom:copyright element SHOULD NOT be used to convey 559 machine-readable licensing information. 561 The atom:copyright element may be assumed to apply to all entries 562 contained by the feed except those entries which contain 563 atom:copyright elements. The atom:copyright element MUST, if 564 present, be considered to apply to the feed as a collection of 565 entries. 567 4.2.9 "atom:info" Element 569 The "atom:info" element is a Content construct that conveys a 570 human-readable explanation of the feed format itself. atom:head 571 elements MAY contain an atom:info element, but MUST NOT contain more 572 than one. 574 The atom:info element SHOULD NOT considered meaningful by processors; 575 it is a convenience to publishers in certain situations. 577 4.2.10 "atom:modified" Element 579 The "atom:modified" element is a Date construct that indicates the 580 time when the state of the feed was last modified, including any 581 changes to entries therein. atom:head elements MUST contain exactly 582 one atom:modified element. 584 The content of an atom:modified element SHOULD have a time zone whose 585 value MUST be "UTC". 587 5. The "atom:entry" Element 589 The "atom:entry" element represents an individual entry. This 590 element can appear as a child of the atom:feed element, or it can 591 appear as the document (i.e., top-level) element of a standalone Atom 592 Entry Document. 594 When appearing in an Atom Entry Document, atom:entry elements MUST 595 have a "version" attribute whose content indicates the version of the 596 Atom specification that the entry conforms to. 598 The version identifier for this specification is 599 "draft-ietf-atompub-format-02: do not deploy". 601 The atom:entry element MAY contain any namespace-qualified 602 [W3C.REC-xml-names-19990114] elements as children. Ordering of the 603 element children of atom:entry element MUST NOT be considered 604 significant. 606 The following child elements are defined by this specification (note 607 that it requires the presence of some of these elements): 609 5.1 "atom:title" Element 611 The "atom:title" element is a Content construct that conveys a 612 human-readable title for the entry. atom:entry elements MUST have 613 exactly one "atom:title" element. 615 5.2 "atom:link" Element 617 The "atom:link" element is a Link construct that conveys a URI 618 associated with the entry. The nature of the relationship as well as 619 the link itself is determined by the element's content. 621 atom:entry elements MUST contain at least one atom:link element with 622 a rel attribute value of "alternate". 624 atom:entry elements MUST NOT contain more than one atom:link element 625 with a rel attribute value of "alternate" that has the same type 626 attribute value. 628 atom:entry elements MAY contain additional atom:link elements beyond 629 those described above. 631 5.3 "atom:author" Element 633 The "atom:author" element is a Person construct that indicates the 634 default author of the entry. atom:entry elements MUST contain 635 exactly one atom:author element, unless, in an Atom Feed Document, 636 the atom:head element contains an atom:author element itself. 637 atom:entry elements MUST NOT contain more than one atom:author 638 element. 640 5.4 "atom:contributor" Element 642 The "atom:contributor" element is a Person construct that indicates a 643 person or other entity who contributes to the entry. atom:entry 644 elements MAY contain one or more atom:contributor elements. 646 5.5 "atom:id" Element 648 The "atom:id" element is an Identity construct that conveys a 649 permanent, universally unique identifier for an entry. atom:entry 650 elements MUST contain exactly one atom:id element. 652 5.6 "atom:updated" Element 654 The "atom:updated" element is a Date construct indicating the most 655 recent instant in time when a change to the entry was made that the 656 publisher wishes to bring to the attention of subscribers. For 657 example, such changes might not include minor adjustments like 658 spelling and grammatical corrections. 660 atom:entry elements MUST contain exactly one atom:updated element. 662 Publishers MAY change the value of this element over time. 663 Processors MAY present entries sorted using this value. Processors 664 MAY choose not to present entries until the instant in time specified 665 in the atom:updated element has passed. 667 5.7 "atom:summary" Element 669 The "atom:summary" element is a Content construct that conveys a 670 short summary, abstract or excerpt of the entry. atom:entry elements 671 MAY contain an atom:summary element, but MUST NOT contain more than 672 one. 674 5.8 "atom:content" Element 676 The "atom:content" element is a Content construct that conveys the 677 content of the entry. atom:entry elements MAY contain one or more 678 atom:content elements. 680 If @type="multipart/alternative", @mode MUST NOT be specified, and 681 content element MUST contain 1 or more content elements. These 682 content elements MUST NOT specify @type="multipart/alternative" (i.e. 684 only one level of nesting is allowed). Consumers SHOULD look at all 685 alternative content elements and determine which one is most 686 suitable, based on which @type and @mode the consumer supports, and 687 preferences specified by the end user (if any). Consumers SHOULD NOT 688 render more than one content alternative. 690 5.9 "atom:copyright" Element 692 The "atom:copyright" element is a Content construct that conveys a 693 human-readable copyright statement for the entry. atom:entry 694 elements MAY contain an atom:copyright element, but MUST NOT contain 695 more than one. 697 The atom:copyright element SHOULD NOT be used to convey 698 machine-readable licensing information. 700 If an atom:entry element does not contain an atom:copyright element, 701 then the atom:copyright element of the containing atom:feed element's 702 atom:head element, if present, should be considered to apply to the 703 entry. 705 5.10 "atom:origin" Element 707 The "atom:origin" element's content conveys the original source of 708 the entry; e.g., the feed where the entry was first published. 710 If the source is an Atom Feed Document, then the content of 711 atom:origin MUST be the same, character-for-character, as that of the 712 atom:id element in that document's atom:head section (i.e., the XPath 713 expression "/atom:feed/atom:head/atom:id"). 715 The content of this element MUST be a URI. atom:entry elements MAY 716 contain an atom:origin element, but MUST NOT contain more than one. 718 6. Managing Feed State 720 [[ talk about what it means to keep a view of a feed ]] 722 7. Securing Atom Documents 724 Because Atom is an XML-based format, existing XML security mechanisms 725 can be used to secure its content. 727 Note that while these mechanisms are available to secure Atom 728 documents, they should not be used indiscriminately. 730 7.1 Digital Signatures 732 The document element of an Atom document (i.e., atom:feed in an Atom 733 Feed Document, atom:entry in an Atom Entry Document) MAY have an 734 Enveloped Signature, as described by XML-Signature and Syntax 735 Processing [W3C.REC-xmldsig-core-20020212]. Other XML signature 736 mechanisms MUST NOT be used on the document element of an Atom 737 document. 739 Processors MUST NOT reject an Atom document containing such a 740 signature because they are not capable of verifying it; they MUST 741 continue processing and MAY inform the user of their failure to 742 validate the signature. 744 In other words, the presence of an element with the namespace URI 745 "http://www.w3.org/2000/09/xmldsig#" and a local name of "Signature" 746 as a child of the document element must not cause a processor to fail 747 merely because of its presence. 749 Other elements in an Atom document MUST NOT be signed unless their 750 defintions explicitly specify such a capability. 752 7.2 Encryption 754 The document element of an Atom document (i.e., atom:feed in an Atom 755 Feed Document, atom:entry in an Atom Entry Document) MAY be 756 encrypted, using the mechanisms described by XML Encryption Syntax 757 and Processing [W3C.REC-xmlenc-core-20021210]. Other XML encryption 758 mechanisms MUST NOT be used on the document element of an Atom 759 document. 761 8. Embedding Atom in Other Formats 763 [[ ... ]] 765 9. Extending Atom 767 [[ ... ]] 769 10. IANA Considerations 771 An Atom Document, when serialized as XML 1.0, can be identified with 772 the following media type: 774 MIME media type name: application 775 MIME subtype name: atom+xml 776 Mandatory parameters: None. 777 Optional parameters: 778 "charset": This parameter has identical semantics to the charset 779 parameter of the "application/xml" media type as specified in 780 RFC 3023 [RFC3023]. [RFC3023]. 781 Encoding considerations: Identical to those of "application/xml" as 782 described in RFC 3023 [RFC3023], section 3.2. 783 Security considerations: As defined in this specification. [[update 784 upon publication]] 785 In addition, as this media type uses the "+xml" convention, it 786 shares the same security considerations as described in RFC 3023 787 [RFC3023], section 10. 788 Interoperability considerations: There are no known interoperability 789 issues. 790 Published specification: This specification. [[update upon 791 publication]] 792 Applications which use this media type: No known applications 793 currently use this media type. 795 Additional information: 797 Magic number(s): As specified for "application/xml" in RFC 3023 798 [RFC3023], section 3.2. 799 File extension: .atom 800 Fragment identifiers: As specified for "application/xml" in RFC 3023 801 [RFC3023], section 5. 802 Base URI: As specified in RFC 3023 [RFC3023], section 6. 803 Macintosh File Type code: TEXT 804 Person and email address to contact for further information: Mark 805 Nottingham 806 Intended usage: COMMON 807 Author/Change controller: This specification's author(s). [[update 808 upon publication]] 810 11. Security Considerations 812 Atom document can be encrypted and signed using 813 [W3C.REC-xmlenc-core-20021210] and [W3C.REC-xmldsig-core-20020212], 814 respectively, and is subject to the security considerations implied 815 by their use. 817 12 Normative References 819 [Atom-autodiscovery] 820 Pilgrim, M., "Atom Feed Autodiscovery", work-in-progress, 821 August 2004. 823 [Atom-protocol] 824 Gregorio, J. and R. Sayre, "The Atom Publishing Protocol", 825 work-in-progress, July 2004. 827 [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail 828 Extensions (MIME) Part One: Format of Internet Message 829 Bodies", RFC 2045, November 1996. 831 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 832 Requirement Levels", BCP 14, RFC 2119, March 1997. 834 [RFC2396] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform 835 Resource Identifiers (URI): Generic Syntax", RFC 2396, 836 August 1998. 838 [RFC2822] Resnick, P., "Internet Message Format", RFC 2822, April 839 2001. 841 [RFC3023] Murata, M., St. Laurent, S. and D. Kohn, "XML Media 842 Types", RFC 3023, January 2001. 844 [RFC3066] Alvestrand, H., "Tags for the Identification of 845 Languages", BCP 47, RFC 3066, January 2001. 847 [RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet: 848 Timestamps", RFC 3339, July 2002. 850 [W3C.NOTE-datetime-19980827] 851 Wolf, M. and C. Wicksteed, "Date and Time Formats", W3C 852 NOTE NOTE-datetime-19980827, August 1998. 854 [W3C.REC-xml-20040204] 855 Yergeau, F., Bray, T., Paoli, J., Sperberg-McQueen, C. and 856 E. Maler, "Extensible Markup Language (XML) 1.0 (Third 857 Edition)", W3C REC REC-xml-20040204, February 2004. 859 [W3C.REC-xml-infoset-20011024] 860 Cowan, J. and R. Tobin, "XML Information Set", W3C REC 861 REC-xml-infoset-20011024, October 2001. 863 [W3C.REC-xml-names-19990114] 864 Bray, T., Hollander, D. and A. Layman, "Namespaces in 865 XML", W3C REC REC-xml-names-19990114, January 1999. 867 [W3C.REC-xmlbase-20010627] 868 Marsh, J., "XML Base", W3C REC REC-xmlbase-20010627, June 869 2001. 871 [W3C.REC-xmldsig-core-20020212] 872 Eastlake, D., Reagle, J. and D. Solo, "XML-Signature 873 Syntax and Processing", W3C REC REC-xmldsig-core-20020212, 874 February 2002. 876 [W3C.REC-xmlenc-core-20021210] 877 Eastlake, D. and J. Reagle, "XML Encryption Syntax and 878 Processing", W3C REC REC-xmlenc-core-20021210, December 879 2002. 881 [1] 883 [2] 885 Author's Address 887 Mark Nottingham (editor) 889 EMail: mnot@pobox.com 890 URI: http://www.mnot.net/ 892 Appendix A. Contributors 894 The following people contributed to preliminary drafts of this 895 document: Tim Bray, Mark Pilgrim, and Sam Ruby. The content and 896 concepts within are a product of the Atom community and the Atom 897 Publishing Format and Protocol Working Group. 899 Appendix B. Revision History 901 [[ this section should be removed before final publication. ]] 903 -02: Removed entry/modified, entry/issued, entry/created; added 904 entry/updated (PaceDateUpdated). 905 Changed date construct from W3C date-time to RFC3339 906 (PaceDateUpdated). 907 Feed links to HTML pages should be reflected back 908 (PaceLinkReflection). 909 Added Identity construct (PaceIdConstruct). 910 Changed feed/id and entry/id to be Identity constructs 911 (PaceIdConstruct). 912 Changed entry/origin's content so that it's the same as the feed's 913 id, rather than its link/@rel="alternate" (PaceIdConstruct). 914 Added "Securing Atom Documents" (PaceDigitalSignatures). 915 -01: Constrained omission of "Information Item" to just elements and 916 attributes. 917 Clarified xml:lang inheritence. 918 Removed entry- and feed-specific langauge about xml:lang (covered 919 by general discussion of xml:lang) 920 Changed xml:lang to reference XML for normative requirements. 921 Changed "... MUST be a string" to "... is unstructued text." 922 Remomved langauge about DOCTYPEs, PIs, Comments, Entities. 923 Changed atom:url to atom:uri, @url to @uri 924 Introduced atom:head 925 Introduced "Atom Feed Document" and "Atom Entry Document". 926 Removed requirement for all elements and attributes to be 927 namespace-qualified; now children of selective elements 928 Added extensibility to Person constructs. 929 Removed requirement for media types to be registered 930 (non-registered media types are legal) 931 Added atom:origin (PaceEntryOrigin) 932 Added requirement for entry/id to be present and a URI 933 (PaceEntryIdRequired). 934 Clarified approach to Comments, PIs and well-formedness, as per 935 RFC3470. 936 Referenced escaping algorithm in XML. 937 Assorted editorial nits and cleanup, refactoring 938 -00: Initial IETF Internet-Draft submission. 939 Added optional version attribute to entry 940 (PaceEntryElementNeedsVersionAttribute). 941 Added hreflang attribute (PaceHrefLang). 942 Clarified inheritence of copyright element (PaceItemCopyright). 943 Added xml:lang to entries (PaceItemLang). 945 Tweaked Infoset-related language (PaceNoInfoSet). 946 Clarified lack of structure in version attribute 947 (PaceVersionAsText). 948 Changed approach to XML Base (PaceXmlBaseEverywhere). 949 Added XML Base processing to atom:id (PaceXmlBaseId). 950 Various editorial cleanup and adjustments for IETF publication. 952 Intellectual Property Statement 954 The IETF takes no position regarding the validity or scope of any 955 Intellectual Property Rights or other rights that might be claimed to 956 pertain to the implementation or use of the technology described in 957 this document or the extent to which any license under such rights 958 might or might not be available; nor does it represent that it has 959 made any independent effort to identify any such rights. Information 960 on the procedures with respect to rights in RFC documents can be 961 found in BCP 78 and BCP 79. 963 Copies of IPR disclosures made to the IETF Secretariat and any 964 assurances of licenses to be made available, or the result of an 965 attempt made to obtain a general license or permission for the use of 966 such proprietary rights by implementers or users of this 967 specification can be obtained from the IETF on-line IPR repository at 968 http://www.ietf.org/ipr. 970 The IETF invites any interested party to bring to its attention any 971 copyrights, patents or patent applications, or other proprietary 972 rights that may cover technology that may be required to implement 973 this standard. Please address the information to the IETF at 974 ietf-ipr@ietf.org. 976 Disclaimer of Validity 978 This document and the information contained herein are provided on an 979 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 980 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET 981 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, 982 INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE 983 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 984 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 986 Copyright Statement 988 Copyright (C) The Internet Society (2004). This document is subject 989 to the rights, licenses and restrictions contained in BCP 78, and 990 except as set forth therein, the authors retain all their rights. 992 Acknowledgment 994 Funding for the RFC Editor function is currently provided by the 995 Internet Society.