From: http://www.mnot.net/drafts/draft-nottingham-atom-format-01.txt Title: The Atom Syndication Format 0.3 (PRE-DRAFT) ------------------------------------------------------------------------- APE (Atom/Pie/Echo) Working Group M. Nottingham, Ed. December 11, 2003 The Atom Syndication Format 0.3 (PRE-DRAFT) Abstract This specification describes version 0.3 of the Atom, an XML-based Web content and metadata syndication format. Editorial Notes This draft HAS NOT been submitted for publication, and does not have any status; it should be referred to as a "pre-draft." Discussion of this draft happens in two fora; The Atom Syntax mailing list [1] The Atom Wiki Web site [2] Comments and suggestions can be directed to the mailing list, whilst active development happens on the Wiki. Sections called out [[like this]] indicate editorial notes that should be removed before final publication. Nottingham [Page 1] Atom Format December 2003 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 4 1.1 Conformance . . . . . . . . . . . . . . . . . . . . . . . 4 1.2 Notational Conventions . . . . . . . . . . . . . . . . . . 4 2. Atom's Use of XML . . . . . . . . . . . . . . . . . . . . 4 3. Common Atom Constructs . . . . . . . . . . . . . . . . . . 4 3.1 Content Constructs . . . . . . . . . . . . . . . . . . . . 4 3.1.1 "type" Attribute . . . . . . . . . . . . . . . . . . . . . 5 3.1.2 "mode" Attribute . . . . . . . . . . . . . . . . . . . . . 5 3.2 Person Constructs . . . . . . . . . . . . . . . . . . . . 5 3.2.1 "atom:name" Element . . . . . . . . . . . . . . . . . . . 5 3.2.2 "atom:url" Element . . . . . . . . . . . . . . . . . . . . 5 3.2.3 "atom:email" Element . . . . . . . . . . . . . . . . . . . 6 3.3 Date Constructs . . . . . . . . . . . . . . . . . . . . . 6 3.4 Link Constructs . . . . . . . . . . . . . . . . . . . . . 6 3.4.1 "rel" Attribute . . . . . . . . . . . . . . . . . . . . . 6 3.4.2 "type" Attribute . . . . . . . . . . . . . . . . . . . . . 6 3.4.3 "href" Attribute . . . . . . . . . . . . . . . . . . . . . 6 3.4.4 "title" Attribute . . . . . . . . . . . . . . . . . . . . 6 4. The "atom:feed" Element . . . . . . . . . . . . . . . . . 7 4.1 "version" Attribute . . . . . . . . . . . . . . . . . . . 7 4.2 "xml:lang" Attribute . . . . . . . . . . . . . . . . . . . 7 4.3 "atom:title" Element . . . . . . . . . . . . . . . . . . . 7 4.4 "atom:link" Element . . . . . . . . . . . . . . . . . . . 7 4.5 "atom:author" Element . . . . . . . . . . . . . . . . . . 8 4.6 "atom:contributor" Element . . . . . . . . . . . . . . . . 8 4.7 "atom:tagline" Element . . . . . . . . . . . . . . . . . . 8 4.8 "atom:id" Element . . . . . . . . . . . . . . . . . . . . 8 4.9 "atom:generator" Element . . . . . . . . . . . . . . . . . 8 4.10 "atom:copyright" Element . . . . . . . . . . . . . . . . . 9 4.11 "atom:info" Element . . . . . . . . . . . . . . . . . . . 9 4.12 "atom:modified" Element . . . . . . . . . . . . . . . . . 9 4.13 "atom:entry" Element . . . . . . . . . . . . . . . . . . . 9 4.13.1 "atom:title" Element . . . . . . . . . . . . . . . . . . . 9 4.13.2 "atom:link" Element . . . . . . . . . . . . . . . . . . . 10 4.13.3 "atom:author" Element . . . . . . . . . . . . . . . . . . 10 4.13.4 "atom:contributor" Element . . . . . . . . . . . . . . . . 10 4.13.5 "atom:id" Element . . . . . . . . . . . . . . . . . . . . 10 4.13.6 "atom:modified" Element . . . . . . . . . . . . . . . . . 10 4.13.7 "atom:issued" Element . . . . . . . . . . . . . . . . . . 11 4.13.8 "atom:created" Element . . . . . . . . . . . . . . . . . . 11 4.13.9 "atom:summary" Element . . . . . . . . . . . . . . . . . . 11 4.13.10 "atom:content" Element . . . . . . . . . . . . . . . . . . 11 5. Managing Feed State . . . . . . . . . . . . . . . . . . . 11 6. Embedding Atom in Other Formats . . . . . . . . . . . . . 11 7. Extending Atom . . . . . . . . . . . . . . . . . . . . . . 11 8. IANA Considerations . . . . . . . . . . . . . . . . . . . 12 Nottingham [Page 2] Atom Format December 2003 9. Security Considerations . . . . . . . . . . . . . . . . . 13 References . . . . . . . . . . . . . . . . . . . . . . . . 13 Author's Address . . . . . . . . . . . . . . . . . . . . . 14 A. Contributors . . . . . . . . . . . . . . . . . . . . . . . 14 B. Revision History . . . . . . . . . . . . . . . . . . . . . 14 Nottingham [Page 3] Atom Format December 2003 1. Introduction Atom is an XML-based file format intended to allow lists of information, known as "feeds", to be synchronised between publishers and consumers. Feeds are composed of a number of items, known as "entries", each with an extensible set of attached metadata. For example, each entry has a title. The primary use case that Atom addresses is for syndicating Web content such as Weblogs and news headlines to other Web sites and directly to consumers. However, nothing precludes it from being used for other purposes and types of content. [[ more motivation / design principles ]] 1.1 Conformance [[ talk about atom documents and atom consumers, and how requirements are placed on them ]] 1.2 Notational Conventions [[ declare namespace prefixes ]] The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 2. Atom's Use of XML [[ talk about namespaces, parsing requirements, etc. / RFC 3023 / use of XML in IETF RFC / xml:base not defined for atom items / xml:lang on any element; determining precedence / namespace: http://purl.org/ atom/ns# / mixed content / extensibility / serialization / what does 'contains' mean? / what does "string" mean? ]] 3. Common Atom Constructs Many of Atom's elements share a few common structures. This section defines their requirements, for convenient reference by the appropriate element definitions. When an element is identified as being a construct, it inherits the corresponding requirements from that construct's definition in this section. 3.1 Content Constructs Nottingham [Page 4] Atom Format December 2003 A Content construct is an element with arbitrary child content, whose properties are described by the following attributes: 3.1.1 "type" Attribute Content constructs MAY have a "type" attribute, whose value indicates the media type of the content. When present, this attribute's value MUST be a registered media type [RFC2045]. If not present, its value MUST be considered to be "text/plain". 3.1.2 "mode" Attribute Content constructs MAY have a "mode" attribute, whose value indicates the method used to encode the content. When present, this attribute's value MUST be listed below. If not present, its value MUST be considered to be "xml". "xml": A mode attribute with the value "xml" indicates that the element's content is inline xml (for example, namespace-qualified XHTML). "escaped": A mode attribute with the value "escaped" indicates that the element's content is an escaped string. Processors MUST unescape the element's content before considering it as content of the indicated media type. "base64": A mode attribute with the value "base64" indicates that the element's content is base64-encoded [RFC2045]. Processors MUST decode the element's content before considering it as content of the the indicated media type. 3.2 Person Constructs A Person construct is an element with the following children: 3.2.1 "atom:name" Element The "atom:name" element's content conveys a human-readable name for the author. It MAY be the name of a corporation or other entity no individual authors can be named. Person constructs MUST contain exactly one "atom:name" element, whose content MUST be a string. 3.2.2 "atom:url" Element The "atom:url" element's content conveys a URI associated with the author. Person constructs MAY contain an atom:url element, but MUST NOT contain more than one. The content of atom:url in a Person Nottingham [Page 5] Atom Format December 2003 construct MUST be a URI [RFC2396]. 3.2.3 "atom:email" Element The "atom:email" element's content conveys an e-mail address associated with the Person construct. Person constructs MAY contain an atom:email element, but MUST NOT contain more than one. Its content MUST be an e-mail address [RFC2822]. Ordering of the element children of Person constructs MUST NOT be considered significant. 3.3 Date Constructs A Date construct is an element whose child content is a W3C Date-Time string [W3C.NOTE-datetime-19980827]. The Date-Time string's time zone SHOULD be "UTC". 3.4 Link Constructs A Link construct is an element that MUST NOT have any child content, and has the following attributes: 3.4.1 "rel" Attribute The "rel" attribute indicates the type of relationship that the link represents. Link constructs MUST have a rel attribute, whose value MUST be a string. 3.4.2 "type" Attribute The "type" attribute indicates an advisory media type; it MAY be used as a hint to determine the type of the representation which should be returned when the URI in the href attribute is dereferenced. Note that the type attribute does not override the actual media type returned with the representation. Link constructs MUST have a type attribute, whose value MUST be a registered media type [RFC2045]. 3.4.3 "href" Attribute The "href" attribute contains the link's URI. Link constructs MUST have a href attribute, whose value MUST be a URI [RFC2396]. 3.4.4 "title" Attribute The "title" attribute conveys human-readable information about the Nottingham [Page 6] Atom Format December 2003 link. Link constructs MAY have a rel attribute, whose value MUST be a string. 4. The "atom:feed" Element The "atom:feed" element is the document (i.e., top-level) element of the format described by this specification. Its children are a (potentially partial) representation of the state of the feed. The atom:feed element MAY contain any namespace-qualified [W3C.REC-xml-names-19990114] elements as children. Ordering of the element children of atom:feed element MUST NOT be considered significant. The following attributes and child elements are defined by this specification (note that it requires the presence of some of these elements): 4.1 "version" Attribute atom:feed elements MUST have a "version" attribute whose content indicates the version of the Atom specification that the construct conforms to. The version identifier for this specification is "0.3". 4.2 "xml:lang" Attribute atom:feed elements SHOULD have an "xml:lang" attribute whose content indicates the default natural language of the feed. The content of this attribute element MUST be [[...ref?]]. 4.3 "atom:title" Element The "atom:title" element is a Content construct that conveys a human-readable title for the feed. atom:feed elements MUST contain exactly one atom:title element. If the feed describes a Web resource, its content SHOULD be the same as that resource's title. 4.4 "atom:link" Element The "atom:link" element is a Link construct that conveys a URI associated with the feed. The nature of the relationship as well as the link itself is determined by the element's content. atom:feed elements MUST contain at least one atom:link element with a rel attribute value of "alternate". Nottingham [Page 7] Atom Format December 2003 atom:feed elements MUST NOT contain more than one atom:link element with a rel attribute value of "alternate" that has the same type attribute value. atom:feed elements MAY contain additional atom:link elements beyond those described above. 4.5 "atom:author" Element The "atom:author" element is a Person construct that indicates the default author of the feed. atom:feed elements MUST contain exactly one atom:author element, UNLESS all of the atom:feed element's child atom:entry elements contain an atom:author element. atom:feed elements MUST NOT contain more than one atom:author element. [[explain inheritence]] 4.6 "atom:contributor" Element The "atom:contributor" element is a Person construct that indicates a person or other entity who contributes to the feed. atom:feed elements MAY contain one or more atom:contributor elements. 4.7 "atom:tagline" Element The "atom:tagline" element is a Content construct that conveys a human-readable description or tagline for the feed. atom:feed elements MAY contain an atom:tagline element, but MUST NOT contain more than one. 4.8 "atom:id" Element The "atom:id" element's content conveys a permanent, globally unique identifier for the feed. It MUST NOT change over time, even if the feed is relocated. atom:feed elements MAY contain an atom:id element, but MUST NOT contain more than one. The content of this element, when present, MUST be a URI. 4.9 "atom:generator" Element The "atom:generator" element's content indentifies the software agent used to generate the feed, for debugging and other purposes. atom:feed elements MAY contain an atom:generator element, but MUST NOT contain more than one. The content of this element, when present, MUST be a string that is a human-readable name for the generating agent. Nottingham [Page 8] Atom Format December 2003 The atom:generator element MAY have a "url" attribute whose value MUST be a URI. When dereferenced, that URI SHOULD produce a representation that is relevant to that agent. The atom:generator element MAY have a "version" attribute that indicates the version of the generating agent. When present, its value MUST be a string. 4.10 "atom:copyright" Element The "atom:copyright" element is Content construct that conveys a human-readable copyright statement for the feed. atom:feed elements MAY contain an atom:copyright element, but MUST NOT contain more than one. The atom:copyright element SHOULD NOT be used to convey machine-readable licensing information. 4.11 "atom:info" Element The "atom:info" element is a Content construct [[what is it for?]]. atom:feed elements MAY contain [[an/one or more]] atom:info element. 4.12 "atom:modified" Element The "atom:modified" element is a Date construct that indicates the time when the state of the feed was last modified, including any changes to entries therein. atom:feed elements MUST contain exactly one atom:modified element. 4.13 "atom:entry" Element The "atom:entry" element's represents an individual entry that is contained by the feed. atom:feed elements MAY contain one or more atom:entry elements. The atom:entry element MAY contain any namespace-qualified [W3C.REC-xml-names-19990114] elements as children. Ordering of the element children of atom:entry element MUST NOT be considered significant. The following child elements are defined by this specification (note that it requires the presence of some of these elements): 4.13.1 "atom:title" Element The "atom:title" element is a Content construct that conveys a human-readable title for the entry. atom:entry elements MUST have Nottingham [Page 9] Atom Format December 2003 exactly one "atom:title" element. If an entry describes a Web resource, its content SHOULD be the same as that resource's title. 4.13.2 "atom:link" Element The "atom:link" element is a Link construct that conveys a URI associated with the entry. The nature of the relationship as well as the link itself is determined by the element's content. atom:entry elements MUST contain at least one atom:link element with a rel attribute value of "alternate". atom:feed elements MUST NOT contain more than one atom:link element with a rel attribute value of "alternate" that has the same type attribute value. atom:entry elements MAY contain additional atom:link elements beyond those described above. 4.13.3 "atom:author" Element The "atom:author" element is a Person construct that indicates the default author of the entry. atom:entry elements MUST contain exactly one atom:author element, UNLESS the atom:feed element containing them contains an atom:author element itself. atom:entry elements MUST NOT contain more than one atom:author element. [[explain inheritence]] 4.13.4 "atom:contributor" Element The "atom:contributor" element is a Person construct that indicates a person or other entity who contributes to the entry. atom:entry elements MAY contain one or more atom:contributor elements. 4.13.5 "atom:id" Element The "atom:id" element's content conveys a permanent, globally unique identifier for the entry. It MUST NOT change over time, even if the entry is relocated. atom:entry elements MUST contain exactly one atom:id element, whose content MUST be a URI. 4.13.6 "atom:modified" Element The "atom:modified" element is a Date construct that indicates the time that the entry was last modified. atom:entry elements MAY contain an atom:modified element, but MUST NOT contain more than one. Nottingham [Page 10] Atom Format December 2003 4.13.7 "atom:issued" Element The "atom:issued" element is a Date construct that indicates the time that the entry was issued. 4.13.8 "atom:created" Element The "atom:created" element is a Date construct that indicates the time that the entry was created. atom:entry elements MAY contain an atom:created element, but MUST NOT contain more than one. If atom:created is not present, its value MUST considered to be the same as that of atom:modified. 4.13.9 "atom:summary" Element The "atom:summary" element is a Content construct that conveys a short summary, description or excerpt of the entry. atom:entry elements MAY contain an atom:created element, but MUST NOT contain more than one. 4.13.10 "atom:content" Element The "atom:content" element is a Content construct that conveys the content of the entry. atom:entry elements MAY contain one or more atom:content elements. If @type="multipart/alternative", @mode MUST NOT be specified, and content element MUST contain 1 or more content elements. These content elements MUST NOT specify @type="multipart/alternative" (i.e. only one level of nesting is allowed). Consumers SHOULD look at all alternative content elements and determine which one is most suitable, based on which @type and @mode the consumer supports, and preferences specified by the end user (if any). Consumers SHOULD NOT render more than one content alternative. 5. Managing Feed State [[ talk about what it means to keep a view of a feed ]] 6. Embedding Atom in Other Formats [[ ... ]] 7. Extending Atom [[ ... ]] Nottingham [Page 11] Atom Format December 2003 8. IANA Considerations The Atom format, when serialized as XML 1.0, can be identified with the following media type: MIME media type name: application MIME subtype name: atom+xml Mandatory parameters: None. Optional parameters: "charset": This parameter has identical semantics to the charset parameter of the "application/xml" media type as specified in RFC 3023 [RFC3023]. [RFC3023]. Encoding considerations: Identical to those of "application/xml" as described in RFC 3023 [RFC3023], section 3.2. Security considerations: As defined in this specification. [[update upon publication]] In addition, as this media type uses the "+xml" convention, it shares the same security considerations as described in RFC 3023 [RFC3023], section 10. Interoperability considerations: There are no known interoperability issues. Published specification: This specification. [[update upon publication]] Applications which use this media type: No known applications currently use this media type. Additional information: Magic number(s): As specified for "application/xml" in RFC 3023 [RFC3023], section 3.2. File extension: .atom Fragment identifiers: As specified for "application/xml" in RFC 3023 [RFC3023], section 5. Nottingham [Page 12] Atom Format December 2003 Base URI: As specified in RFC 3023 [RFC3023], section 6. Macintosh File Type code: TEXT Person and email address to contact for further information: Mark Nottingham Intended usage: COMMON Author/Change controller: This specification's author(s). [[update upon publication]] 9. Security Considerations [[ this is required ]] References [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies", RFC 2045, November 1996. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2396] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource Identifiers (URI): Generic Syntax", RFC 2396, August 1998. [RFC2822] Resnick, P., "Internet Message Format", RFC 2822, April 2001. [RFC3023] Murata, M., St. Laurent, S. and D. Kohn, "XML Media Types", RFC 3023, January 2001. [W3C.NOTE-datetime-19980827] Wolf, M. and C. Wicksteed, "Date and Time Formats", W3C NOTE NOTE-datetime-19980827, August 1998. [W3C.REC-xml-names-19990114] Bray, T., Hollander, D. and A. Layman, "Namespaces in XML", W3C REC REC-xml-names-19990114, January 1999. [1] [2] Nottingham [Page 13] Atom Format December 2003 Author's Address Mark Nottingham (editor) EMail: mnot@pobox.com URI: http://www.mnot.net/ Appendix A. Contributors The following people contributed to this specification's content: Tim Bray, Mark Pilgrim, and Sam Ruby. The content and concepts within are a product of the Atom community. Appendix B. Revision History 2003-12-11: New format for atom:generator. New format for atom:link. Many elements are now Content constructs. Made it explicit that ordering in containers isn't significant. Added references. Added media type registration template. Reorganization. Nottingham [Page 14]