draft-ietf-atompub-format-01.txt   draft-ietf-atompub-format-02.txt 
Network Working Group M. Nottingham, Ed. Network Working Group M. Nottingham, Ed.
Expires: January 15, 2005 Expires: March 6, 2005
The Atom Syndication Format The Atom Syndication Format
draft-ietf-atompub-format-01 draft-ietf-atompub-format-02
Status of this Memo Status of this Memo
By submitting this Internet-Draft, I certify that any applicable By submitting this Internet-Draft, I certify that any applicable
patent or other IPR claims of which I am aware have been disclosed, patent or other IPR claims of which I am aware have been disclosed,
and any of which I become aware will be disclosed, in accordance with and any of which I become aware will be disclosed, in accordance with
RFC 3668. RFC 3668.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
This Internet-Draft will expire on January 15, 2005. This Internet-Draft will expire on March 6, 2005.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved. Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract Abstract
This specification describes Atom, an XML-based Web content and This document specifies Atom, an XML-based Web content and metadata
metadata syndication format. syndication format.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Editorial Notes . . . . . . . . . . . . . . . . . . . . . 4 1.1 Editorial Notes . . . . . . . . . . . . . . . . . . . . . 4
1.2 Example . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.2 Example . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3 Conformance . . . . . . . . . . . . . . . . . . . . . . . 5 1.3 Conformance . . . . . . . . . . . . . . . . . . . . . . . 5
1.4 Notational Conventions . . . . . . . . . . . . . . . . . . 5 1.4 Notational Conventions . . . . . . . . . . . . . . . . . . 5
2. Atom Documents . . . . . . . . . . . . . . . . . . . . . . . 7 2. Atom Documents . . . . . . . . . . . . . . . . . . . . . . . 7
3. Common Atom Constructs . . . . . . . . . . . . . . . . . . . 9 3. Common Atom Constructs . . . . . . . . . . . . . . . . . . . 9
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3.2.1 "atom:name" Element . . . . . . . . . . . . . . . . . 10 3.2.1 "atom:name" Element . . . . . . . . . . . . . . . . . 10
3.2.2 "atom:uri" Element . . . . . . . . . . . . . . . . . . 10 3.2.2 "atom:uri" Element . . . . . . . . . . . . . . . . . . 10
3.2.3 "atom:email" Element . . . . . . . . . . . . . . . . . 10 3.2.3 "atom:email" Element . . . . . . . . . . . . . . . . . 10
3.3 Date Constructs . . . . . . . . . . . . . . . . . . . . . 10 3.3 Date Constructs . . . . . . . . . . . . . . . . . . . . . 10
3.4 Link Constructs . . . . . . . . . . . . . . . . . . . . . 10 3.4 Link Constructs . . . . . . . . . . . . . . . . . . . . . 10
3.4.1 "rel" Attribute . . . . . . . . . . . . . . . . . . . 10 3.4.1 "rel" Attribute . . . . . . . . . . . . . . . . . . . 10
3.4.2 "type" Attribute . . . . . . . . . . . . . . . . . . . 11 3.4.2 "type" Attribute . . . . . . . . . . . . . . . . . . . 11
3.4.3 "href" Attribute . . . . . . . . . . . . . . . . . . . 11 3.4.3 "href" Attribute . . . . . . . . . . . . . . . . . . . 11
3.4.4 "hreflang" Attribute . . . . . . . . . . . . . . . . . 11 3.4.4 "hreflang" Attribute . . . . . . . . . . . . . . . . . 11
3.4.5 "title" Attribute . . . . . . . . . . . . . . . . . . 11 3.4.5 "title" Attribute . . . . . . . . . . . . . . . . . . 11
4. The "atom:feed" Element . . . . . . . . . . . . . . . . . . 12 3.5 Identity Constructs . . . . . . . . . . . . . . . . . . . 11
4.1 "version" Attribute . . . . . . . . . . . . . . . . . . . 12 3.5.1 Dereferencing Identity Constructs . . . . . . . . . . 11
4.2 The "atom:head" Element . . . . . . . . . . . . . . . . . 12 3.5.2 Comparing Identity Constructs . . . . . . . . . . . . 12
4.2.1 "atom:title" Element . . . . . . . . . . . . . . . . . 12 4. The "atom:feed" Element . . . . . . . . . . . . . . . . . . 13
4.2.2 "atom:link" Element . . . . . . . . . . . . . . . . . 12 4.1 "version" Attribute . . . . . . . . . . . . . . . . . . . 13
4.2.3 "atom:author" Element . . . . . . . . . . . . . . . . 13 4.2 The "atom:head" Element . . . . . . . . . . . . . . . . . 13
4.2.4 "atom:contributor" Element . . . . . . . . . . . . . . 13 4.2.1 "atom:title" Element . . . . . . . . . . . . . . . . . 13
4.2.5 "atom:tagline" Element . . . . . . . . . . . . . . . . 13 4.2.2 "atom:link" Element . . . . . . . . . . . . . . . . . 13
4.2.6 "atom:id" Element . . . . . . . . . . . . . . . . . . 13 4.2.3 "atom:author" Element . . . . . . . . . . . . . . . . 14
4.2.7 "atom:generator" Element . . . . . . . . . . . . . . . 13 4.2.4 "atom:contributor" Element . . . . . . . . . . . . . . 14
4.2.8 "atom:copyright" Element . . . . . . . . . . . . . . . 14 4.2.5 "atom:tagline" Element . . . . . . . . . . . . . . . . 14
4.2.9 "atom:info" Element . . . . . . . . . . . . . . . . . 14 4.2.6 "atom:id" Element . . . . . . . . . . . . . . . . . . 14
4.2.10 "atom:modified" Element . . . . . . . . . . . . . . 14 4.2.7 "atom:generator" Element . . . . . . . . . . . . . . . 14
5. The "atom:entry" Element . . . . . . . . . . . . . . . . . . 15 4.2.8 "atom:copyright" Element . . . . . . . . . . . . . . . 15
5.1 "atom:title" Element . . . . . . . . . . . . . . . . . . . 15 4.2.9 "atom:info" Element . . . . . . . . . . . . . . . . . 15
5.2 "atom:link" Element . . . . . . . . . . . . . . . . . . . 15 4.2.10 "atom:modified" Element . . . . . . . . . . . . . . 15
5.3 "atom:author" Element . . . . . . . . . . . . . . . . . . 15 5. The "atom:entry" Element . . . . . . . . . . . . . . . . . . 16
5.4 "atom:contributor" Element . . . . . . . . . . . . . . . . 16 5.1 "atom:title" Element . . . . . . . . . . . . . . . . . . . 16
5.5 "atom:id" Element . . . . . . . . . . . . . . . . . . . . 16 5.2 "atom:link" Element . . . . . . . . . . . . . . . . . . . 16
5.6 "atom:modified" Element . . . . . . . . . . . . . . . . . 16 5.3 "atom:author" Element . . . . . . . . . . . . . . . . . . 16
5.7 "atom:issued" Element . . . . . . . . . . . . . . . . . . 16 5.4 "atom:contributor" Element . . . . . . . . . . . . . . . . 17
5.8 "atom:created" Element . . . . . . . . . . . . . . . . . . 16 5.5 "atom:id" Element . . . . . . . . . . . . . . . . . . . . 17
5.9 "atom:summary" Element . . . . . . . . . . . . . . . . . . 17 5.6 "atom:updated" Element . . . . . . . . . . . . . . . . . . 17
5.10 "atom:content" Element . . . . . . . . . . . . . . . . . 17 5.7 "atom:summary" Element . . . . . . . . . . . . . . . . . . 17
5.11 "atom:copyright" Element . . . . . . . . . . . . . . . . 17 5.8 "atom:content" Element . . . . . . . . . . . . . . . . . . 17
5.12 "atom:origin" Element . . . . . . . . . . . . . . . . . 17 5.9 "atom:copyright" Element . . . . . . . . . . . . . . . . . 18
5.10 "atom:origin" Element . . . . . . . . . . . . . . . . . 18
6. Managing Feed State . . . . . . . . . . . . . . . . . . . . 19 6. Managing Feed State . . . . . . . . . . . . . . . . . . . . 19
7. Embedding Atom in Other Formats . . . . . . . . . . . . . . 20 7. Securing Atom Documents . . . . . . . . . . . . . . . . . . 20
8. Extending Atom . . . . . . . . . . . . . . . . . . . . . . . 21 7.1 Digital Signatures . . . . . . . . . . . . . . . . . . . . 20
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . 22 7.2 Encryption . . . . . . . . . . . . . . . . . . . . . . . . 20
10. Security Considerations . . . . . . . . . . . . . . . . . . 23 8. Embedding Atom in Other Formats . . . . . . . . . . . . . . 21
11. Normative References . . . . . . . . . . . . . . . . . . . . 23 9. Extending Atom . . . . . . . . . . . . . . . . . . . . . . . 22
Author's Address . . . . . . . . . . . . . . . . . . . . . . 24 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . 23
A. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 25 11. Security Considerations . . . . . . . . . . . . . . . . . . 24
B. Revision History . . . . . . . . . . . . . . . . . . . . . . 26 12. Normative References . . . . . . . . . . . . . . . . . . . . 24
Intellectual Property and Copyright Statements . . . . . . . 27 Author's Address . . . . . . . . . . . . . . . . . . . . . . 25
A. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 26
B. Revision History . . . . . . . . . . . . . . . . . . . . . . 27
Intellectual Property and Copyright Statements . . . . . . . 29
1. Introduction 1. Introduction
Atom is an XML-based document format intended to allow lists of Atom is an XML-based document format intended to allow lists of
related information, known as "feeds", to be synchronised between related information, known as "feeds", to be synchronised between
publishers and consumers. Feeds are composed of a number of items, publishers and consumers. Feeds are composed of a number of items,
known as "entries", each with an extensible set of attached metadata. known as "entries", each with an extensible set of attached metadata.
For example, each entry has a title. For example, each entry has a title.
The primary use case that Atom addresses is the syndication of Web The primary use case that Atom addresses is the syndication of Web
content such as Weblogs and news headlines, to Web sites as well as content such as Weblogs and news headlines to Web sites as well as
directly to user agents. However, nothing precludes it from being directly to user agents. However, nothing precludes it from being
used for other purposes and kinds of content. used for other purposes and kinds of content.
Details of comunication protocols between software agents using Atom Details of comunication protocols between software agents using Atom
can be found in the Atom Protocol specification [Atom-protocol]. can be found in the Atom Protocol specification [Atom-protocol].
[[ more motivation / design principles ]] [[ more motivation / design principles ]]
1.1 Editorial Notes 1.1 Editorial Notes
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This document is an early draft and known to be incomplete. Topics This document is an early draft and known to be incomplete. Topics
marked [[like this]] indicate where additional text is likely to be marked [[like this]] indicate where additional text is likely to be
added. added.
1.2 Example 1.2 Example
A minimal, single-entry Atom Feed Document: A minimal, single-entry Atom Feed Document:
<?xml version="1.0" encoding="utf-8"?> <?xml version="1.0" encoding="utf-8"?>
<feed version="draft-ietf-atompub-format-01: do not deploy" <feed version="draft-ietf-atompub-format-02: do not deploy"
xmlns="http://purl.org/atom/ns#draft-ietf-atompub-format-01"> xmlns="http://purl.org/atom/ns#draft-ietf-atompub-format-02">
<head> <head>
<title>Example Feed</title> <title>Example Feed</title>
<link rel="alternate" type="text/html" <link rel="alternate" type="text/html"
href="http://example.org/index.atom"/> href="http://example.org/"/>
<modified>2003-12-13T18:30:02Z</modified> <modified>2003-12-13T18:30:02Z</modified>
<author> <author>
<name>John Doe</name> <name>John Doe</name>
</author> </author>
</head> </head>
<entry> <entry>
<title>Atom-Powered Robots Run Amok</title> <title>Atom-Powered Robots Run Amok</title>
<link rel="alternate" type="text/html" <link rel="alternate" type="text/html"
href="http://example.org/2003/12/13/atom03"/> href="http://example.org/2003/12/13/atom03"/>
<id>tag:example.org,2003:3.2397</id> <id>tag:example.org,2003:3.2397</id>
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1.3 Conformance 1.3 Conformance
[[ talk about atom documents and atom consumers, and how requirements [[ talk about atom documents and atom consumers, and how requirements
are placed on them ]] are placed on them ]]
1.4 Notational Conventions 1.4 Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in BCP 14, [RFC2119].
This specification uses XML Namespaces [W3C.REC-xml-names-19990114] This specification uses XML Namespaces [W3C.REC-xml-names-19990114]
to uniquely identify XML elements and attribute names. It uses the to uniquely identify XML elements and attribute names. It uses the
following namespace prefixes for the indicated namespace URIs; following namespace prefixes for the indicated namespace URIs;
"atom": http://purl.org/atom/ns#draft-ietf-atompub-format-01 "atom": http://purl.org/atom/ns#draft-ietf-atompub-format-02
Note that the choice of any namespace prefix is arbitrary and not Note that the choice of any namespace prefix is arbitrary and not
semantically significant. semantically significant.
Atom is specified using terms from the XML Infoset Atom is specified using terms from the XML Infoset
[W3C.REC-xml-infoset-20011024]. However, this specification uses a [W3C.REC-xml-infoset-20011024]. However, this specification uses a
shorthand for two common terms; the phrase "Information Item" is shorthand for two common terms; the phrase "Information Item" is
omitted when naming Element Information Items and Attribute omitted when naming Element Information Items and Attribute
Information Items. Information Items.
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relative URI reference present in an Atom document. This includes relative URI reference present in an Atom document. This includes
such elements and attributes as specified by Atom itself, as well as such elements and attributes as specified by Atom itself, as well as
those specified by extensions to Atom. those specified by extensions to Atom.
Any element in an Atom Document MAY have an xml:lang attribute, whose Any element in an Atom Document MAY have an xml:lang attribute, whose
content indicates the default natural language of the element's content indicates the default natural language of the element's
content. Requirements regarding the content and interpretation of content. Requirements regarding the content and interpretation of
xml:lang are specified in XML 1.0 [W3C.REC-xml-20040204] Section xml:lang are specified in XML 1.0 [W3C.REC-xml-20040204] Section
2.12. For convenience, the most important are summarised here: 2.12. For convenience, the most important are summarised here:
The content of this attribute must be a language tag [RFC3066] or o The content of this attribute must be a language tag [RFC3066] or
an empty string (e.g., xml:lang=""), which indicates that there is an empty string (e.g., xml:lang=""), which indicates that there is
no language information available. no language information available.
If an element does not have an xml:lang element, the first o If an element does not have an xml:lang element, the first
xml:lang attribute in its ancestors indicates the natural language xml:lang attribute in its ancestors indicates the natural language
of its content. of its content.
[[ feedback as to whether this listing is helpful or not would be [[ feedback as to whether this listing is helpful or not would be
appreciated; re-stating the requirements of other specifications is appreciated; re-stating the requirements of other specifications is
tricky. ]] tricky. ]]
[[ discussion of URI escaping and i18n ]] [[ discussion of URI escaping and i18n ]]
[[ discussion of white space ]] [[ discussion of white space ]]
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Content constructs MAY have a "type" attribute, whose value indicates Content constructs MAY have a "type" attribute, whose value indicates
the media type of the content. When present, this attribute's value the media type of the content. When present, this attribute's value
MUST be a media type [RFC2045]. If this attribute is not present, MUST be a media type [RFC2045]. If this attribute is not present,
processors MUST behave as if it were present with a value of "text/ processors MUST behave as if it were present with a value of "text/
plain". plain".
3.1.2 "mode" Attribute 3.1.2 "mode" Attribute
Content constructs MAY have a "mode" attribute, whose value indicates Content constructs MAY have a "mode" attribute, whose value indicates
the method used to encode the content. When present, this the method used to encode the content. When present, this
attribute's value MUST be listed below. If not present, its value attribute's value MUST be listed below. If not present, processors
MUST be considered to be "xml". MUST behave as if its value were "xml".
"xml": A mode attribute with the value "xml" indicates that the "xml": A mode attribute with the value "xml" indicates that the
element's content is inline xml (for example, namespace-qualified element's content is inline xml (for example, namespace-qualified
XHTML). XHTML).
"escaped": A mode attribute with the value "escaped" indicates that "escaped": A mode attribute with the value "escaped" indicates that
the element's content is escaped, as defined in the element's content is escaped, as defined in
[W3C.REC-xml-20040204] (section 4.6). Processors MUST unescape [W3C.REC-xml-20040204] (section 4.6). Processors MUST unescape
the element's content before considering it as content of the the element's content before considering it as content of the
indicated media type. indicated media type.
"base64": A mode attribute with the value "base64" indicates that "base64": A mode attribute with the value "base64" indicates that
the element's content is base64-encoded [RFC2045]. Processors the element's content is base64-encoded [RFC2045]. Processors
MUST decode the element's content before considering it as content MUST decode the element's content before considering it as content
of the the indicated media type. of the the indicated media type.
3.2 Person Constructs 3.2 Person Constructs
A Person construct is an element that describes a person, A Person construct is an element that describes a person,
corporation, or similar entity. It has the following children: corporation, or similar entity.
Person constructs MAY be extended by namespace-qualified element
children.
Ordering of the element children of Person constructs MUST NOT be
considered significant.
3.2.1 "atom:name" Element 3.2.1 "atom:name" Element
The "atom:name" element's content conveys a human-readable name for The "atom:name" element's content conveys a human-readable name for
the person. Person constructs MUST contain exactly one "atom:name" the person. Person constructs MUST contain exactly one "atom:name"
element, whose content is unstructured text. element.
3.2.2 "atom:uri" Element 3.2.2 "atom:uri" Element
The "atom:uri" element's content conveys a URI associated with the The "atom:uri" element's content conveys a URI associated with the
person. Person constructs MAY contain an atom:uri element, but MUST person. Person constructs MAY contain an atom:uri element, but MUST
NOT contain more than one. The content of atom:uri in a Person NOT contain more than one. The content of atom:uri in a Person
construct MUST be a URI [RFC2396]. construct MUST be a URI [RFC2396].
xml:base [W3C.REC-xmlbase-20010627] processing MUST be applied to the xml:base [W3C.REC-xmlbase-20010627] processing MUST be applied to the
atom:uri element's content. atom:uri element's content.
3.2.3 "atom:email" Element 3.2.3 "atom:email" Element
The "atom:email" element's content conveys an e-mail address The "atom:email" element's content conveys an e-mail address
associated with the persons. Person constructs MAY contain an associated with the persons. Person constructs MAY contain an
atom:email element, but MUST NOT contain more than one. Its content atom:email element, but MUST NOT contain more than one. Its content
MUST be an e-mail address [RFC2822]. MUST be an e-mail address [RFC2822].
Person constructs MAY be extended by namespace-qualified element
children.
Ordering of the element children of Person constructs MUST NOT be
considered significant.
3.3 Date Constructs 3.3 Date Constructs
A Date construct is an element whose content is a W3C Date-Time A Date construct is an element whose content MUST conform to the
string [W3C.NOTE-datetime-19980827]. date-time BNF rule in [RFC3339].
3.4 Link Constructs 3.4 Link Constructs
A Link construct is an element that MUST NOT have any child content, A Link construct is an element that MUST NOT have any child content,
and has the following attributes: and has the following attributes:
3.4.1 "rel" Attribute 3.4.1 "rel" Attribute
The "rel" attribute indicates the type of relationship that the link The "rel" attribute indicates the type of relationship that the link
represents. Link constructs MUST have a rel attribute, whose value represents. Link constructs MUST have a rel attribute, whose value
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The "hreflang" attribute's content describes the language of the The "hreflang" attribute's content describes the language of the
resource pointed to by the href attribute. When used together with resource pointed to by the href attribute. When used together with
the rel="alternate", it implies a translated version of the entry. the rel="alternate", it implies a translated version of the entry.
Link constructs MAY have an hreflang attribute, whose value MUST be a Link constructs MAY have an hreflang attribute, whose value MUST be a
language tag [RFC3066]. language tag [RFC3066].
3.4.5 "title" Attribute 3.4.5 "title" Attribute
The "title" attribute conveys human-readable information about the The "title" attribute conveys human-readable information about the
link. Link constructs MAY have a title attribute, whose value is link. Link constructs MAY have a title attribute.
unstructured text.
3.5 Identity Constructs
An Identity construct is an element whose content conveys a
permanent, universally unique identifier for the construct's parent.
Its content MUST be an absolute URI [RFC2396] that is universally
unique; i.e., it MUST NOT change over time, even if the parent feed
or entry element is relocated, migrated, syndicated, republished,
exported or imported.
3.5.1 Dereferencing Identity Constructs
The content of an Identity construct MAY be dereferencable (e.g. a
HTTP URI). However, processors MUST NOT assume it to be
dereferencable.
If the identified resource is served dynamically, the content of an
Identity construct MUST be created only once and then stored along
with the resource. The content of an Identity construct MUST NOT be
created dynamically.
Because of the risk of confusion between URIs that would be
equivalent if dereferenced, the following normalization strategy is
strongly encouraged when generating Identity constructs:
o Provide the scheme in lowercase characters.
o Provide the host, if any, in lowercase characters.
o Only perform percent-encoding where it is essential.
o Use uppercase A-through-F characters when percent-encoding.
o Prevent dot-segments appearing in paths.
o For schemes that define a default authority, use an empty
authority if the default is desired.
o For schemes that define an empty path to be equivalent to a path
of "/", use "/".
o For schemes that define a port, use an empty port if the default
is desired.
o Preserve empty fragment identifiers and queries.
o Ensure that all portions of the URI are utf-8 encoded NFC form
Unicode strings.
3.5.2 Comparing Identity Constructs
Instances of Identity constructs can be compared to determine whether
a entry or feed is the same as one seen before. Processors MUST
compare Identity constructs on a character-by-character basis in a
case-sensitive fashion.
As a result, two URIs that resolve to the same resource but are not
character-for-character identical will be considered different for
the purposes of Identifier comparison.
For example, "http://www.example.org/thing",
"http://www.example.org/Thing", "http://www.EXAMPLE.org/thing" and
"HTTP://www.example.org/thing" will all be considered different
identifiers, despite their differences in case.
Likewise, "http://www.example.com/~bob",
"http://www.example.com/%7ebob" and "http://www.example.com/%7Ebob"
will all be considered different identifiers, because URI %-escaping
is significant for the purposes of comparison.
XML character and entity references MUST be converted into characters
before comparison.
4. The "atom:feed" Element 4. The "atom:feed" Element
The "atom:feed" element is the document (i.e., top-level) element of The "atom:feed" element is the document (i.e., top-level) element of
an Atom Feed Document, acting as a container for metadata and data an Atom Feed Document, acting as a container for metadata and data
associated with the feed. Its first element child MUST be atom:head, associated with the feed. Its first element child MUST be atom:head,
which MAY be followed zero or more atom:entry child elements. which MAY be followed zero or more atom:entry child elements.
4.1 "version" Attribute 4.1 "version" Attribute
atom:feed elements MUST have a "version" attribute whose content atom:feed elements MUST have a "version" attribute whose content
indicates the version of the Atom specification that the feed indicates the version of the Atom specification that the feed
conforms to. The content of this attribute is unstructured text. conforms to. The content of this attribute is unstructured text.
The version identifier for this specification is The version identifier for this specification is
"draft-ietf-atompub-format-01: do not deploy". "draft-ietf-atompub-format-02: do not deploy".
4.2 The "atom:head" Element 4.2 The "atom:head" Element
The atom:head element acts as a container for metadata about the feed The atom:head element acts as a container for metadata about the feed
itself. itself.
The atom:head element MAY contain any namespace-qualified The atom:head element MAY contain any namespace-qualified
[W3C.REC-xml-names-19990114] elements as children. Ordering of the [W3C.REC-xml-names-19990114] elements as children. Ordering of the
element children of atom:head element MUST NOT be considered element children of atom:head element MUST NOT be considered
significant. significant.
skipping to change at page 12, line 43 skipping to change at page 13, line 43
4.2.1 "atom:title" Element 4.2.1 "atom:title" Element
The "atom:title" element is a Content construct that conveys a The "atom:title" element is a Content construct that conveys a
human-readable title for the feed. atom:head elements MUST contain human-readable title for the feed. atom:head elements MUST contain
exactly one atom:title element. exactly one atom:title element.
4.2.2 "atom:link" Element 4.2.2 "atom:link" Element
The "atom:link" element is a Link construct that conveys a URI The "atom:link" element is a Link construct that conveys a URI
associated with the feed. The nature of the relationship as well as associated with the feed. The nature of the relationship is
the link itself is determined by the element's content. determined by the construct's rel attribute.
atom:head elements MUST contain at least one atom:link element with a atom:head elements MUST contain at least one atom:link element with a
rel attribute value of "alternate". rel attribute value of "alternate".
atom:head elements MUST NOT contain more than one atom:link element atom:head elements MUST NOT contain more than one atom:link element
with a rel attribute value of "alternate" that has the same type with a rel attribute value of "alternate" that has the same type
attribute value. attribute value.
If a feed's atom:link element with type="alternate" resolves to an
HTML document, then that document SHOULD have a autodiscovery link
element [Atom-autodiscovery] that reflects back to the feed.
atom:head elements MAY contain additional atom:link elements beyond atom:head elements MAY contain additional atom:link elements beyond
those described above. those described above.
4.2.3 "atom:author" Element 4.2.3 "atom:author" Element
The "atom:author" element is a Person construct that indicates the The "atom:author" element is a Person construct that indicates the
default author of the feed. atom:head elements MUST contain exactly default author of the feed. atom:head elements MUST contain exactly
one atom:author element, UNLESS all of the atom:feed element's child one atom:author element, UNLESS all of the atom:feed element's child
atom:entry elements contain an atom:author element. atom:head atom:entry elements contain an atom:author element. atom:head
elements MUST NOT contain more than one atom:author element. elements MUST NOT contain more than one atom:author element.
skipping to change at page 13, line 33 skipping to change at page 14, line 37
4.2.5 "atom:tagline" Element 4.2.5 "atom:tagline" Element
The "atom:tagline" element is a Content construct that conveys a The "atom:tagline" element is a Content construct that conveys a
human-readable description or tagline for the feed. atom:head human-readable description or tagline for the feed. atom:head
elements MAY contain an atom:tagline element, but MUST NOT contain elements MAY contain an atom:tagline element, but MUST NOT contain
more than one. more than one.
4.2.6 "atom:id" Element 4.2.6 "atom:id" Element
The "atom:id" element's content conveys a permanent, globally unique The "atom:id" element is an Identity construct that conveys a
identifier for the feed. It MUST NOT change over time, even if the permanent, universally unique identifier for a feed. atom:head
feed is relocated. atom:head elements MAY contain an atom:id elements MAY contain an atom:id element, but MUST NOT contain more
element, but MUST NOT contain more than one. The content of this than one.
element, when present, MUST be a URI.
xml:base [W3C.REC-xmlbase-20010627] processing MUST be applied to the
atom:id element's content.
4.2.7 "atom:generator" Element 4.2.7 "atom:generator" Element
The "atom:generator" element's content indentifies the software agent The "atom:generator" element's content indentifies the software agent
used to generate the feed, for debugging and other purposes. used to generate the feed, for debugging and other purposes.
atom:head elements MAY contain an atom:generator element, but MUST atom:head elements MAY contain an atom:generator element, but MUST
NOT contain more than one. NOT contain more than one.
The content of this element, when present, MUST be a string that is a The content of this element, when present, MUST be a string that is a
human-readable name for the generating agent. human-readable name for the generating agent.
skipping to change at page 15, line 17 skipping to change at page 16, line 17
The "atom:entry" element represents an individual entry. This The "atom:entry" element represents an individual entry. This
element can appear as a child of the atom:feed element, or it can element can appear as a child of the atom:feed element, or it can
appear as the document (i.e., top-level) element of a standalone Atom appear as the document (i.e., top-level) element of a standalone Atom
Entry Document. Entry Document.
When appearing in an Atom Entry Document, atom:entry elements MUST When appearing in an Atom Entry Document, atom:entry elements MUST
have a "version" attribute whose content indicates the version of the have a "version" attribute whose content indicates the version of the
Atom specification that the entry conforms to. Atom specification that the entry conforms to.
The version identifier for this specification is The version identifier for this specification is
"draft-ietf-atompub-format-01: do not deploy". "draft-ietf-atompub-format-02: do not deploy".
The atom:entry element MAY contain any namespace-qualified The atom:entry element MAY contain any namespace-qualified
[W3C.REC-xml-names-19990114] elements as children. Ordering of the [W3C.REC-xml-names-19990114] elements as children. Ordering of the
element children of atom:entry element MUST NOT be considered element children of atom:entry element MUST NOT be considered
significant. significant.
The following child elements are defined by this specification (note The following child elements are defined by this specification (note
that it requires the presence of some of these elements): that it requires the presence of some of these elements):
5.1 "atom:title" Element 5.1 "atom:title" Element
skipping to change at page 16, line 17 skipping to change at page 17, line 17
element. element.
5.4 "atom:contributor" Element 5.4 "atom:contributor" Element
The "atom:contributor" element is a Person construct that indicates a The "atom:contributor" element is a Person construct that indicates a
person or other entity who contributes to the entry. atom:entry person or other entity who contributes to the entry. atom:entry
elements MAY contain one or more atom:contributor elements. elements MAY contain one or more atom:contributor elements.
5.5 "atom:id" Element 5.5 "atom:id" Element
The "atom:id" element's content conveys a permanent, globally unique The "atom:id" element is an Identity construct that conveys a
identifier for the entry. It MUST NOT change over time, even if permanent, universally unique identifier for an entry. atom:entry
other representations of the entry (such as a web representation elements MUST contain exactly one atom:id element.
pointed to by the entry's atom:link element) are relocated.
For a given entry, the atom:id element's content MUST be stable
across all Atom Documents published by the same entity.
atom:entry MUST contain exactly one atom:id element. The content of
this element MUST be a URI.
5.6 "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".
5.7 "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.
5.8 "atom:created" Element 5.6 "atom:updated" Element
The "atom:created" element is a Date construct that indicates the The "atom:updated" element is a Date construct indicating the most
time that the entry was created. atom:entry elements MAY contain an recent instant in time when a change to the entry was made that the
atom:created element, but MUST NOT contain more than one. publisher wishes to bring to the attention of subscribers. For
example, such changes might not include minor adjustments like
spelling and grammatical corrections.
The content of an atom:created element MUST have a time zone whose atom:entry elements MUST contain exactly one atom:updated element.
value SHOULD be "UTC".
If atom:created is not present, its content MUST considered to be the Publishers MAY change the value of this element over time.
same as that of atom:modified. Processors MAY present entries sorted using this value. Processors
MAY choose not to present entries until the instant in time specified
in the atom:updated element has passed.
5.9 "atom:summary" Element 5.7 "atom:summary" Element
The "atom:summary" element is a Content construct that conveys a The "atom:summary" element is a Content construct that conveys a
short summary, abstract or excerpt of the entry. atom:entry elements short summary, abstract or excerpt of the entry. atom:entry elements
MAY contain an atom:summary element, but MUST NOT contain more than MAY contain an atom:summary element, but MUST NOT contain more than
one. one.
5.10 "atom:content" Element 5.8 "atom:content" Element
The "atom:content" element is a Content construct that conveys the The "atom:content" element is a Content construct that conveys the
content of the entry. atom:entry elements MAY contain one or more content of the entry. atom:entry elements MAY contain one or more
atom:content elements. atom:content elements.
If @type="multipart/alternative", @mode MUST NOT be specified, and If @type="multipart/alternative", @mode MUST NOT be specified, and
content element MUST contain 1 or more content elements. These content element MUST contain 1 or more content elements. These
content elements MUST NOT specify @type="multipart/alternative" (i.e. content elements MUST NOT specify @type="multipart/alternative" (i.e.
only one level of nesting is allowed). Consumers SHOULD look at all only one level of nesting is allowed). Consumers SHOULD look at all
alternative content elements and determine which one is most alternative content elements and determine which one is most
suitable, based on which @type and @mode the consumer supports, and suitable, based on which @type and @mode the consumer supports, and
preferences specified by the end user (if any). Consumers SHOULD NOT preferences specified by the end user (if any). Consumers SHOULD NOT
render more than one content alternative. render more than one content alternative.
5.11 "atom:copyright" Element 5.9 "atom:copyright" Element
The "atom:copyright" element is a Content construct that conveys a The "atom:copyright" element is a Content construct that conveys a
human-readable copyright statement for the entry. atom:entry human-readable copyright statement for the entry. atom:entry
elements MAY contain an atom:copyright element, but MUST NOT contain elements MAY contain an atom:copyright element, but MUST NOT contain
more than one. more than one.
The atom:copyright element SHOULD NOT be used to convey The atom:copyright element SHOULD NOT be used to convey
machine-readable licensing information. machine-readable licensing information.
If an atom:entry element does not contain an atom:copyright element, If an atom:entry element does not contain an atom:copyright element,
then the atom:copyright element of the containing atom:feed element's then the atom:copyright element of the containing atom:feed element's
atom:head element, if present, should be considered to apply to the atom:head element, if present, should be considered to apply to the
entry. entry.
5.12 "atom:origin" Element 5.10 "atom:origin" Element
The "atom:origin" element's content conveys the original source of The "atom:origin" element's content conveys the original source of
the entry; e.g., the feed where the entry was first published. the entry; e.g., the feed where the entry was first published.
If the source is an Atom Feed Document, then the content of If the source is an Atom Feed Document, then the content of
atom:origin MUST be the same, character-for-character, as that of the atom:origin MUST be the same, character-for-character, as that of the
href attribute of the atom:link element that has a rel attribute atom:id element in that document's atom:head section (i.e., the XPath
value of "alternate" in that document's atom:head section (i.e., the expression "/atom:feed/atom:head/atom:id").
XPath expression "/atom:feed/atom:head/atom:link[@rel='alternate']/
@href").
The content of this element MUST be a URI. atom:entry elements MAY The content of this element MUST be a URI. atom:entry elements MAY
contain an atom:origin element, but MUST NOT contain more than one. contain an atom:origin element, but MUST NOT contain more than one.
6. Managing Feed State 6. Managing Feed State
[[ talk about what it means to keep a view of a feed ]] [[ talk about what it means to keep a view of a feed ]]
7. Embedding Atom in Other Formats 7. Securing Atom Documents
Because Atom is an XML-based format, existing XML security mechanisms
can be used to secure its content.
Note that while these mechanisms are available to secure Atom
documents, they should not be used indiscriminately.
7.1 Digital Signatures
The document element of an Atom document (i.e., atom:feed in an Atom
Feed Document, atom:entry in an Atom Entry Document) MAY have an
Enveloped Signature, as described by XML-Signature and Syntax
Processing [W3C.REC-xmldsig-core-20020212]. Other XML signature
mechanisms MUST NOT be used on the document element of an Atom
document.
Processors MUST NOT reject an Atom document containing such a
signature because they are not capable of verifying it; they MUST
continue processing and MAY inform the user of their failure to
validate the signature.
In other words, the presence of an element with the namespace URI
"http://www.w3.org/2000/09/xmldsig#" and a local name of "Signature"
as a child of the document element must not cause a processor to fail
merely because of its presence.
Other elements in an Atom document MUST NOT be signed unless their
defintions explicitly specify such a capability.
7.2 Encryption
The document element of an Atom document (i.e., atom:feed in an Atom
Feed Document, atom:entry in an Atom Entry Document) MAY be
encrypted, using the mechanisms described by XML Encryption Syntax
and Processing [W3C.REC-xmlenc-core-20021210]. Other XML encryption
mechanisms MUST NOT be used on the document element of an Atom
document.
8. Embedding Atom in Other Formats
[[ ... ]] [[ ... ]]
8. Extending Atom 9. Extending Atom
[[ ... ]] [[ ... ]]
9. IANA Considerations 10. IANA Considerations
An Atom Document, when serialized as XML 1.0, can be identified with An Atom Document, when serialized as XML 1.0, can be identified with
the following media type: the following media type:
MIME media type name: application MIME media type name: application
MIME subtype name: atom+xml MIME subtype name: atom+xml
Mandatory parameters: None. Mandatory parameters: None.
Optional parameters: Optional parameters:
"charset": This parameter has identical semantics to the charset "charset": This parameter has identical semantics to the charset
parameter of the "application/xml" media type as specified in parameter of the "application/xml" media type as specified in
skipping to change at page 23, line 5 skipping to change at page 24, line 5
Fragment identifiers: As specified for "application/xml" in RFC 3023 Fragment identifiers: As specified for "application/xml" in RFC 3023
[RFC3023], section 5. [RFC3023], section 5.
Base URI: As specified in RFC 3023 [RFC3023], section 6. Base URI: As specified in RFC 3023 [RFC3023], section 6.
Macintosh File Type code: TEXT Macintosh File Type code: TEXT
Person and email address to contact for further information: Mark Person and email address to contact for further information: Mark
Nottingham <mnot@pobox.com> Nottingham <mnot@pobox.com>
Intended usage: COMMON Intended usage: COMMON
Author/Change controller: This specification's author(s). [[update Author/Change controller: This specification's author(s). [[update
upon publication]] upon publication]]
10. Security Considerations 11. Security Considerations
[[ this is required ]] Atom document can be encrypted and signed using
[W3C.REC-xmlenc-core-20021210] and [W3C.REC-xmldsig-core-20020212],
respectively, and is subject to the security considerations implied
by their use.
11 Normative References 12 Normative References
[Atom-autodiscovery]
Pilgrim, M., "Atom Feed Autodiscovery", work-in-progress,
August 2004.
[Atom-protocol] [Atom-protocol]
Gregorio, J. and R. Sayre, "The Atom Publishing Protocol", Gregorio, J. and R. Sayre, "The Atom Publishing Protocol",
work-in-progress, July 2004. work-in-progress, July 2004.
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996. Bodies", RFC 2045, November 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
skipping to change at page 23, line 35 skipping to change at page 24, line 42
[RFC2822] Resnick, P., "Internet Message Format", RFC 2822, April [RFC2822] Resnick, P., "Internet Message Format", RFC 2822, April
2001. 2001.
[RFC3023] Murata, M., St. Laurent, S. and D. Kohn, "XML Media [RFC3023] Murata, M., St. Laurent, S. and D. Kohn, "XML Media
Types", RFC 3023, January 2001. Types", RFC 3023, January 2001.
[RFC3066] Alvestrand, H., "Tags for the Identification of [RFC3066] Alvestrand, H., "Tags for the Identification of
Languages", BCP 47, RFC 3066, January 2001. Languages", BCP 47, RFC 3066, January 2001.
[RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet:
Timestamps", RFC 3339, July 2002.
[W3C.NOTE-datetime-19980827] [W3C.NOTE-datetime-19980827]
Wolf, M. and C. Wicksteed, "Date and Time Formats", W3C Wolf, M. and C. Wicksteed, "Date and Time Formats", W3C
NOTE NOTE-datetime-19980827, August 1998. NOTE NOTE-datetime-19980827, August 1998.
[W3C.REC-xml-20040204] [W3C.REC-xml-20040204]
Yergeau, F., Bray, T., Paoli, J., Sperberg-McQueen, C. and Yergeau, F., Bray, T., Paoli, J., Sperberg-McQueen, C. and
E. Maler, "Extensible Markup Language (XML) 1.0 (Third E. Maler, "Extensible Markup Language (XML) 1.0 (Third
Edition)", W3C REC REC-xml-20040204, February 2004. Edition)", W3C REC REC-xml-20040204, February 2004.
[W3C.REC-xml-infoset-20011024] [W3C.REC-xml-infoset-20011024]
skipping to change at page 24, line 7 skipping to change at page 25, line 17
REC-xml-infoset-20011024, October 2001. REC-xml-infoset-20011024, October 2001.
[W3C.REC-xml-names-19990114] [W3C.REC-xml-names-19990114]
Bray, T., Hollander, D. and A. Layman, "Namespaces in Bray, T., Hollander, D. and A. Layman, "Namespaces in
XML", W3C REC REC-xml-names-19990114, January 1999. XML", W3C REC REC-xml-names-19990114, January 1999.
[W3C.REC-xmlbase-20010627] [W3C.REC-xmlbase-20010627]
Marsh, J., "XML Base", W3C REC REC-xmlbase-20010627, June Marsh, J., "XML Base", W3C REC REC-xmlbase-20010627, June
2001. 2001.
[W3C.REC-xmldsig-core-20020212]
Eastlake, D., Reagle, J. and D. Solo, "XML-Signature
Syntax and Processing", W3C REC REC-xmldsig-core-20020212,
February 2002.
[W3C.REC-xmlenc-core-20021210]
Eastlake, D. and J. Reagle, "XML Encryption Syntax and
Processing", W3C REC REC-xmlenc-core-20021210, December
2002.
[1] <http://www.imc.org/atom-syntax/index.html> [1] <http://www.imc.org/atom-syntax/index.html>
[2] <http://www.intertwingly.net/wiki/pie/FrontPage> [2] <http://www.intertwingly.net/wiki/pie/FrontPage>
Author's Address Author's Address
Mark Nottingham (editor) Mark Nottingham (editor)
EMail: mnot@pobox.com EMail: mnot@pobox.com
URI: http://www.mnot.net/ URI: http://www.mnot.net/
skipping to change at page 26, line 9 skipping to change at page 27, line 9
The following people contributed to preliminary drafts of this The following people contributed to preliminary drafts of this
document: Tim Bray, Mark Pilgrim, and Sam Ruby. The content and document: Tim Bray, Mark Pilgrim, and Sam Ruby. The content and
concepts within are a product of the Atom community and the Atom concepts within are a product of the Atom community and the Atom
Publishing Format and Protocol Working Group. Publishing Format and Protocol Working Group.
Appendix B. Revision History Appendix B. Revision History
[[ this section should be removed before final publication. ]] [[ this section should be removed before final publication. ]]
-02: Removed entry/modified, entry/issued, entry/created; added
entry/updated (PaceDateUpdated).
Changed date construct from W3C date-time to RFC3339
(PaceDateUpdated).
Feed links to HTML pages should be reflected back
(PaceLinkReflection).
Added Identity construct (PaceIdConstruct).
Changed feed/id and entry/id to be Identity constructs
(PaceIdConstruct).
Changed entry/origin's content so that it's the same as the feed's
id, rather than its link/@rel="alternate" (PaceIdConstruct).
Added "Securing Atom Documents" (PaceDigitalSignatures).
-01: Constrained omission of "Information Item" to just elements and -01: Constrained omission of "Information Item" to just elements and
attributes. attributes.
Clarified xml:lang inheritence. Clarified xml:lang inheritence.
Removed entry- and feed-specific langauge about xml:lang (covered Removed entry- and feed-specific langauge about xml:lang (covered
by general discussion of xml:lang) by general discussion of xml:lang)
Changed xml:lang to reference XML for normative requirements. Changed xml:lang to reference XML for normative requirements.
Changed "... MUST be a string" to "... is unstructued text." Changed "... MUST be a string" to "... is unstructued text."
Remomved langauge about DOCTYPEs, PIs, Comments, Entities. Remomved langauge about DOCTYPEs, PIs, Comments, Entities.
Changed atom:url to atom:uri, @url to @uri Changed atom:url to atom:uri, @url to @uri
Introduced atom:head Introduced atom:head
 End of changes. 

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