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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.
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970 The IETF invites any interested party to bring to its attention any
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976 Disclaimer of Validity
978 This document and the information contained herein are provided on an
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986 Copyright Statement
988 Copyright (C) The Internet Society (2004). This document is subject
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992 Acknowledgment
994 Funding for the RFC Editor function is currently provided by the
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