The Atom Syndication Format 0.3 (PRE-DRAFT)
Flowers In December
TOC
APE (Atom/Pie/Echo) Working Group M Nottingham
December 2003
The Atom Syndication Format 0.3 (PRE-DRAFT)
draft-nottingham-atom-format-02
Abstract
This specification describes version 0.3 of the Atom, an XML-based Web
content and metadata syndication format.
Editorial Notes
This draft is made available for historical purposes only; DO NOT
implement it or ship products conforming to it. This work has migrated
to the ATOMPUB Working Group in the IETF.
Discussion of this draft happens in two fora;
The Atom Syntax mailing list
The Atom Wiki Web site
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.
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RFC
TOC
Table of Contents
1 Introduction
1.1 Example
1.2 Conformance
1.3 Notational Conventions
2 Atom Documents
3 Common Atom Constructs
3.1 Content Constructs
3.1.1 "type" Attribute
3.1.2 "mode" Attribute
3.2 Person Constructs
3.2.1 "atom:name" Element
3.2.2 "atom:url" Element
3.2.3 "atom:email" Element
3.3 Date Constructs
3.4 Link Constructs
3.4.1 "rel" Attribute
3.4.2 "type" Attribute
3.4.3 "href" Attribute
3.4.4 "title" Attribute
4 The "atom:feed" Element
4.1 "version" Attribute
4.2 "xml:lang" Attribute
4.3 "atom:title" Element
4.4 "atom:link" Element
4.5 "atom:author" Element
4.6 "atom:contributor" Element
4.7 "atom:tagline" Element
4.8 "atom:id" Element
4.9 "atom:generator" Element
4.10 "atom:copyright" Element
4.11 "atom:info" Element
4.12 "atom:modified" Element
4.13 "atom:entry" Element
4.13.1 "atom:title" Element
4.13.2 "atom:link" Element
4.13.3 "atom:author" Element
4.13.4 "atom:contributor" Element
4.13.5 "atom:id" Element
4.13.6 "atom:modified" Element
4.13.7 "atom:issued" Element
4.13.8 "atom:created" Element
4.13.9 "atom:summary" Element
4.13.10 "atom:content" Element
5 Managing Feed State
6 Embedding Atom in Other Formats
7 Extending Atom
8 IANA Considerations
9 Security Considerations
§ References
§ Author's Address
A Contributors
B Revision History
§ Full Copyright Statement
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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.
Details of comunication protocols between software agents using Atom
are to be found in the Atom API specification
<eref>http://bitworking.org/projects/atom/draft-gregorio-09.html</eref>.
[[ more motivation / design principles ]]
1.1 Example
A minimal, single-entry Atom feed serialized as XML 1.0:
<?xml version="1.0" encoding="utf-8"?>
<feed version="0.3" xmlns="http://purl.org/atom/ns#">
<title>dive into mark</title>
<link rel="alternate" type="text/html"
href="http://diveintomark.org/"/>
<modified>2003-12-13T18:30:02Z</modified>
<author>
<name>Mark Pilgrim</name>
</author>
<entry>
<title>Atom 0.3 snapshot</title>
<link rel="alternate" type="text/html"
href="http://diveintomark.org/2003/12/13/atom03"/>
<id>tag:diveintomark.org,2003:3.2397</id>
<issued>2003-12-13T08:29:29-04:00</issued>
<modified>2003-12-13T18:30:02Z</modified>
</entry>
</feed>
1.2 Conformance
[[ talk about atom documents and atom consumers, and how requirements
are placed on them ]]
1.3 Notational Conventions
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].
This specification uses XML Namespaces [W3C.REC-xml-names-19990114] to
uniquely identify XML elements and attribute names. It uses the
following namespace prefixes for the indicated namespace URIs;
"atom":
http://purl.org/atom/ns#
Note that the choice of any namespace prefix is arbitrary and not
semantically significant.
Atom is specified using the XML Infoset [W3C.REC-xml-infoset-20011024],
but uses a shorthand for common terms; the phrase "Information Item" is
not used when naming XML constructs.
Therefore, when this specification uses the term "element," it is
refering to an Element Information Item in Infoset terms. Likewise,
when it uses the term "attribute," it is refering to an Attribute
Information Item.
Furthermore, when it indicates that the content of an element or
attribute is a "string," it is referring to a set of one or more
Character Information Items.
[[children / contains]]
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2 Atom Documents
An Atom document is an XML document whose document element is the
atom:feed element, as described below.
Atom is specified in terms of the XML Infoset, and therefore may be
serialized in a variety of fashions. However, the canonical
serialization of an Atom document is XML 1.0, and this is the only
serialization that can be identified with the "application/atom+xml"
media type.
Atom documents MAY have a Document Type Declaration.
[[Entities]]
Atom documents SHOULD NOT contain Processing Instructions, unless they
are a commonly used convention outside the scope of Atom (e.g., the PI
for XSLT processing).
Atom documents MAY contain Comments wherever they are legal in XML.
All elements and attributes in an Atom document MUST be
namespace-qualified. Note that this requirement does not preclude the
use of a default namespace.
Any element in an Atom document MAY have an xml:base attribute.
However, XML Base [W3C.REC-xmlbase-20010627] processing MUST NOT be
applied to element or attribute content, unless that element or
attribute's specification explicitly includes XML Base processing.
Any element MAY have an xml:lang attribute whose content indicates the
default natural language of the element's content. The content of this
attribute element MUST be a registered language tag [RFC3066]. When
determining element content's natural language, the first xml:lang
attribute encountered in that element's ancestors MUST be used.
[[extensibility]]
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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
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 construct
MUST be a URI [RFC2396].
xml:base [W3C.REC-xmlbase-20010627] processing MUST be applied to the
atom:url element.
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].
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, and MUST be one of the values enumerated in the Atom API
specification
<eref>http://bitworking.org/projects/atom/draft-gregorio-09.html</eref>.
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].
xml:base [W3C.REC-xmlbase-20010627] processing MUST be applied to the
atom:url element.
3.4.4 "title" Attribute
The "title" attribute conveys human-readable information about the
link. Link constructs MAY have a title attribute, whose value MUST be a
string.
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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 a registered language tag [RFC3066].
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".
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.
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 that conveys a
human-readable explanation of the feed format itself. atom:feed
elements MAY contain an atom:info element, but MUST NOT contain more
than one.
The atom:info element SHOULD NOT considered meaningful by processors;
it is a convenience to publishers in certain situations.
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.
The content of an atom:modified element SHOULD have a time zone whose
value MUST be "UTC".
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
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:entry 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 other
representations of the entry (such as a web representation pointed to
by the entry's atom:link element) are relocated. If the same entry is
syndicated in two atom:feeds published by the same entity, the entry's
atom:id MUST be the same in both feeds.
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 MUST contain an
atom:modified element, but MUST NOT contain more than one.
The content of an atom:modified element MUST have a time zone whose
value SHOULD be "UTC".
4.13.7 "atom:issued" Element
The "atom:issued" element is a Date construct that indicates the time
that the entry was issued. atom:entry elements MUST contain an
atom:issued element, but MUST NOT contain more than one.
The content of an atom:issued element MAY omit a time zone.
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.
The content of an atom:created element MUST have a time zone whose
value SHOULD be "UTC".
If atom:created is not present, its content 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, abstract 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.
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5 Managing Feed State
[[ talk about what it means to keep a view of a feed ]]
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6 Embedding Atom in Other Formats
[[ ... ]]
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7 Extending Atom
[[ ... ]]
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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.
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 <mn...@pobox.com>
Intended usage:
COMMON
Author/Change controller:
This specification's author(s). [[update upon publication]]
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9 Security Considerations
[[ this is required ]]
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References
[RFC2045] Freed, N. and Borenstein, N.S., "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.T. and Masinter, L., "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 Kohn, D., "XML Media Types",
RFC 3023, January 2001.
[RFC3066] Alvestrand, H., "Tags for the Identification of Languages",
BCP 47, RFC 3066, January 2001.
[W3C.NOTE-datetime-19980827] Wolf, M and Wicksteed, C, "Date and Time
Formats", W3C NOTE NOTE-datetime-19980827, August 1998.
[W3C.REC-xml-infoset-20011024] Cowan, J and Tobin, R, "XML Information
Set", W3C REC REC-xml-infoset-20011024, October 2001.
[W3C.REC-xml-names-19990114] Bray, T, Hollander, D and Layman, A,
"Namespaces in XML", W3C REC REC-xml-names-19990114, January 1999.
[W3C.REC-xmlbase-20010627] Marsh, J, "XML Base", W3C REC
REC-xmlbase-20010627, June 2001.
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Author's Address
Mark Nottingham
EMail: mn...@pobox.com
URI: http://www.mnot.net/
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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.
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B Revision History
2003-12-12 (-02):
Fixed several typos, clarified some langauge.
Reference to RFC3066 for language tags.
Explained purpose, clarified requirements of atom:info.
Relaxed requirements for atom:issued date.
Added reference to API spec.
Added example.
Expanded upon Atom's use of XML (now "Atom Documents").
Expanded upon notational conventions.
Added xml:base requirements to atom:author, atom:link.
Adjusted time zone requirements for dates.
rel attribute values are constrained to those listed in the Atom API.
2003-12-11 (-01):
New format for atom:generator.
New format for atom:link.
Added atom:info
Many elements are now Content constructs.
Made it explicit that ordering in containers isn't significant.
Added references.
Added media type registration template.
Reorganization.