Network Working Group M. Nottingham, Ed.
Internet-Draft September 5, 2004
Expires: March 6, 2005
The Atom Syndication Format
draft-ietf-atompub-format-02
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Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This document specifies Atom, an XML-based Web content and metadata
syndication format.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1 Editorial Notes . . . . . . . . . . . . . . . . . . . . . 4
1.2 Example . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3 Conformance . . . . . . . . . . . . . . . . . . . . . . . 5
1.4 Notational Conventions . . . . . . . . . . . . . . . . . . 5
2. Atom Documents . . . . . . . . . . . . . . . . . . . . . . . 7
3. Common Atom Constructs . . . . . . . . . . . . . . . . . . . 9
3.1 Content Constructs . . . . . . . . . . . . . . . . . . . . 9
3.1.1 "type" Attribute . . . . . . . . . . . . . . . . . . . 9
3.1.2 "mode" Attribute . . . . . . . . . . . . . . . . . . . 9
3.2 Person Constructs . . . . . . . . . . . . . . . . . . . . 9
3.2.1 "atom:name" Element . . . . . . . . . . . . . . . . . 10
3.2.2 "atom:uri" Element . . . . . . . . . . . . . . . . . . 10
3.2.3 "atom:email" Element . . . . . . . . . . . . . . . . . 10
3.3 Date Constructs . . . . . . . . . . . . . . . . . . . . . 10
3.4 Link Constructs . . . . . . . . . . . . . . . . . . . . . 10
3.4.1 "rel" Attribute . . . . . . . . . . . . . . . . . . . 10
3.4.2 "type" Attribute . . . . . . . . . . . . . . . . . . . 11
3.4.3 "href" Attribute . . . . . . . . . . . . . . . . . . . 11
3.4.4 "hreflang" Attribute . . . . . . . . . . . . . . . . . 11
3.4.5 "title" Attribute . . . . . . . . . . . . . . . . . . 11
3.5 Identity Constructs . . . . . . . . . . . . . . . . . . . 11
3.5.1 Dereferencing Identity Constructs . . . . . . . . . . 11
3.5.2 Comparing Identity Constructs . . . . . . . . . . . . 12
4. The "atom:feed" Element . . . . . . . . . . . . . . . . . . 13
4.1 "version" Attribute . . . . . . . . . . . . . . . . . . . 13
4.2 The "atom:head" Element . . . . . . . . . . . . . . . . . 13
4.2.1 "atom:title" Element . . . . . . . . . . . . . . . . . 13
4.2.2 "atom:link" Element . . . . . . . . . . . . . . . . . 13
4.2.3 "atom:author" Element . . . . . . . . . . . . . . . . 14
4.2.4 "atom:contributor" Element . . . . . . . . . . . . . . 14
4.2.5 "atom:tagline" Element . . . . . . . . . . . . . . . . 14
4.2.6 "atom:id" Element . . . . . . . . . . . . . . . . . . 14
4.2.7 "atom:generator" Element . . . . . . . . . . . . . . . 14
4.2.8 "atom:copyright" Element . . . . . . . . . . . . . . . 15
4.2.9 "atom:info" Element . . . . . . . . . . . . . . . . . 15
4.2.10 "atom:modified" Element . . . . . . . . . . . . . . 15
5. The "atom:entry" Element . . . . . . . . . . . . . . . . . . 16
5.1 "atom:title" Element . . . . . . . . . . . . . . . . . . . 16
5.2 "atom:link" Element . . . . . . . . . . . . . . . . . . . 16
5.3 "atom:author" Element . . . . . . . . . . . . . . . . . . 16
5.4 "atom:contributor" Element . . . . . . . . . . . . . . . . 17
5.5 "atom:id" Element . . . . . . . . . . . . . . . . . . . . 17
5.6 "atom:updated" Element . . . . . . . . . . . . . . . . . . 17
5.7 "atom:summary" Element . . . . . . . . . . . . . . . . . . 17
5.8 "atom:content" Element . . . . . . . . . . . . . . . . . . 17
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5.9 "atom:copyright" Element . . . . . . . . . . . . . . . . . 18
5.10 "atom:origin" Element . . . . . . . . . . . . . . . . . 18
6. Managing Feed State . . . . . . . . . . . . . . . . . . . . 19
7. Securing Atom Documents . . . . . . . . . . . . . . . . . . 20
7.1 Digital Signatures . . . . . . . . . . . . . . . . . . . . 20
7.2 Encryption . . . . . . . . . . . . . . . . . . . . . . . . 20
8. Embedding Atom in Other Formats . . . . . . . . . . . . . . 21
9. Extending Atom . . . . . . . . . . . . . . . . . . . . . . . 22
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . 23
11. Security Considerations . . . . . . . . . . . . . . . . . . 24
12. Normative References . . . . . . . . . . . . . . . . . . . . 24
Author's Address . . . . . . . . . . . . . . . . . . . . . . 25
A. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 26
B. Revision History . . . . . . . . . . . . . . . . . . . . . . 27
Intellectual Property and Copyright Statements . . . . . . . 29
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1. Introduction
Atom is an XML-based document format intended to allow lists of
related 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 the syndication of Web
content such as Weblogs and news headlines to Web sites as well as
directly to user agents. However, nothing precludes it from being
used for other purposes and kinds of content.
Details of comunication protocols between software agents using Atom
can be found in the Atom Protocol specification [Atom-protocol].
[[ more motivation / design principles ]]
1.1 Editorial Notes
The Atom format is a work-in-progress, and this draft is both
incomplete and likely to change rapidly. As a result, THE FORMAT
DESCRIBED BY THIS DRAFT SHOULD NOT BE DEPLOYED, either in production
systems or in any non-experimental fashion on the Internet.
Discussion of this draft happens in two fora;
The mailing list [1]
The Atom Wiki Web site [2]
Active development takes place on the mailing list, while the Wiki is
used for issue tracking and new proposals.
This document is an early draft and known to be incomplete. Topics
marked [[like this]] indicate where additional text is likely to be
added.
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1.2 Example
A minimal, single-entry Atom Feed Document:
Example Feed2003-12-13T18:30:02ZJohn DoeAtom-Powered Robots Run Amoktag:example.org,2003:3.23972003-12-13T08:29:29-04:002003-12-13T18:30:02Z
1.3 Conformance
[[ talk about atom documents and atom consumers, and how requirements
are placed on them ]]
1.4 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 BCP 14, [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#draft-ietf-atompub-format-02
Note that the choice of any namespace prefix is arbitrary and not
semantically significant.
Atom is specified using terms from the XML Infoset
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[W3C.REC-xml-infoset-20011024]. However, this specification uses a
shorthand for two common terms; the phrase "Information Item" is
omitted when naming Element Information Items and Attribute
Information Items.
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.
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2. Atom Documents
This specification describes two kinds of Atom Documents; Atom Feed
Documents and Atom Entry Documents.
An Atom Feed Document is a representation of an Atom feed, including
metadata about the feed, and some or all of the entries associated
with it. Its document element is atom:feed.
An Atom Entry Document represents exactly one Atom Entry, outside of
the context of an Atom Feed. Its document element is atom:entry.
Both kinds of Atom documents are specified in terms of the XML
Information Set, serialised as XML 1.0 [W3C.REC-xml-20040204] and
identified with the "application/atom+xml" media type. Atom
Documents MUST be well-formed XML.
[[ Validity? ]]
Atom constrains the appearance and content of elements and
attributes; unless otherwise stated, Atom Documents MAY contain other
Information Items as appropriate. In particular, Comment Information
Items and Processing Instruction Information Items SHOULD be ignored
in the normal processing of an Atom Document.
Any element in an Atom Document MAY have an xml:base attribute. XML
Base [W3C.REC-xmlbase-20010627] processing MUST be applied to any
relative URI reference present in an Atom document. This includes
such elements and attributes as specified by Atom itself, as well as
those specified by extensions to Atom.
Any element in an Atom Document MAY have an xml:lang attribute, whose
content indicates the default natural language of the element's
content. Requirements regarding the content and interpretation of
xml:lang are specified in XML 1.0 [W3C.REC-xml-20040204] Section
2.12. For convenience, the most important are summarised here:
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
no language information available.
o If an element does not have an xml:lang element, the first
xml:lang attribute in its ancestors indicates the natural language
of its content.
[[ feedback as to whether this listing is helpful or not would be
appreciated; re-stating the requirements of other specifications is
tricky. ]]
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[[ discussion of URI escaping and i18n ]]
[[ discussion of white space ]]
Atom is extensible. See the section titled 'Extending Atom' later in
this document for a full description of how Atom Documents can be
extended.
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3. Common Atom Constructs
Many of Atom's elements share a few common structures. This section
defines a few such structures and their requirements, for convenient
reference by the appropriate element definitions.
When an element is identified as being a particular kind of
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 media type [RFC2045]. If this attribute is not present,
processors MUST behave as if it were present with a value of "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, processors
MUST behave as if its value were "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 escaped, as defined in
[W3C.REC-xml-20040204] (section 4.6). 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 that describes a person,
corporation, or similar entity.
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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
The "atom:name" element's content conveys a human-readable name for
the person. Person constructs MUST contain exactly one "atom:name"
element.
3.2.2 "atom:uri" Element
The "atom:uri" element's content conveys a URI associated with the
person. Person constructs MAY contain an atom:uri element, but MUST
NOT contain more than one. The content of atom:uri in a Person
construct MUST be a URI [RFC2396].
xml:base [W3C.REC-xmlbase-20010627] processing MUST be applied to the
atom:uri element's content.
3.2.3 "atom:email" Element
The "atom:email" element's content conveys an e-mail address
associated with the persons. Person constructs MAY contain an
atom:email element, but MUST NOT contain more than one. Its content
MUST be an e-mail address [RFC2822].
3.3 Date Constructs
A Date construct is an element whose content MUST conform to the
date-time BNF rule in [RFC3339].
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 one of the values enumerated in the Atom Protocol
specification [Atom-protocol].
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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
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
href attribute's content.
3.4.4 "hreflang" Attribute
The "hreflang" attribute's content describes the language of the
resource pointed to by the href attribute. When used together with
the rel="alternate", it implies a translated version of the entry.
Link constructs MAY have an hreflang attribute, whose value MUST be a
language tag [RFC3066].
3.4.5 "title" Attribute
The "title" attribute conveys human-readable information about the
link. Link constructs MAY have a title attribute.
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.
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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.
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4. The "atom:feed" Element
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
associated with the feed. Its first element child MUST be atom:head,
which MAY be followed zero or more atom:entry child elements.
4.1 "version" Attribute
atom:feed elements MUST have a "version" attribute whose content
indicates the version of the Atom specification that the feed
conforms to. The content of this attribute is unstructured text.
The version identifier for this specification is
"draft-ietf-atompub-format-02: do not deploy".
4.2 The "atom:head" Element
The atom:head element acts as a container for metadata about the feed
itself.
The atom:head element MAY contain any namespace-qualified
[W3C.REC-xml-names-19990114] elements as children. Ordering of the
element children of atom:head element MUST NOT be considered
significant.
The following child elements are defined by this specification (note
that the presence of some of these elements is required):
4.2.1 "atom:title" Element
The "atom:title" element is a Content construct that conveys a
human-readable title for the feed. atom:head elements MUST contain
exactly one atom:title element.
4.2.2 "atom:link" Element
The "atom:link" element is a Link construct that conveys a URI
associated with the feed. The nature of the relationship is
determined by the construct's rel attribute.
atom:head elements MUST contain at least one atom:link element with a
rel attribute value of "alternate".
atom:head elements MUST NOT contain more than one atom:link element
with a rel attribute value of "alternate" that has the same type
attribute value.
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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
those described above.
4.2.3 "atom:author" Element
The "atom:author" element is a Person construct that indicates the
default author of the feed. atom:head 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:head
elements MUST NOT contain more than one atom:author element.
[[explain inheritence]]
4.2.4 "atom:contributor" Element
The "atom:contributor" element is a Person construct that indicates a
person or other entity who contributes to the feed. atom:head
elements MAY contain one or more atom:contributor elements.
4.2.5 "atom:tagline" Element
The "atom:tagline" element is a Content construct that conveys a
human-readable description or tagline for the feed. atom:head
elements MAY contain an atom:tagline element, but MUST NOT contain
more than one.
4.2.6 "atom:id" Element
The "atom:id" element is an Identity construct that conveys a
permanent, universally unique identifier for a feed. atom:head
elements MAY contain an atom:id element, but MUST NOT contain more
than one.
4.2.7 "atom:generator" Element
The "atom:generator" element's content indentifies the software agent
used to generate the feed, for debugging and other purposes.
atom:head 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 "uri" attribute whose value
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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 is unstructured text.
4.2.8 "atom:copyright" Element
The "atom:copyright" element is Content construct that conveys a
human-readable copyright statement for the feed. atom:head 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.
The atom:copyright element may be assumed to apply to all entries
contained by the feed except those entries which contain
atom:copyright elements. The atom:copyright element MUST, if
present, be considered to apply to the feed as a collection of
entries.
4.2.9 "atom:info" Element
The "atom:info" element is a Content construct that conveys a
human-readable explanation of the feed format itself. atom:head
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.
4.2.10 "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:head 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".
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5. The "atom:entry" Element
The "atom:entry" element represents an individual entry. This
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
Entry Document.
When appearing in an Atom Entry Document, atom:entry elements MUST
have a "version" attribute whose content indicates the version of the
Atom specification that the entry conforms to.
The version identifier for this specification is
"draft-ietf-atompub-format-02: do not deploy".
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):
5.1 "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.
5.2 "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.
5.3 "atom:author" Element
The "atom:author" element is a Person construct that indicates the
default author of the entry. atom:entry elements MUST contain
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exactly one atom:author element, unless, in an Atom Feed Document,
the atom:head element contains an atom:author element itself.
atom:entry elements MUST NOT contain more than one atom:author
element.
5.4 "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.
5.5 "atom:id" Element
The "atom:id" element is an Identity construct that conveys a
permanent, universally unique identifier for an entry. atom:entry
elements MUST contain exactly one atom:id element.
5.6 "atom:updated" Element
The "atom:updated" element is a Date construct indicating the most
recent instant in time when a change to the entry was made that the
publisher wishes to bring to the attention of subscribers. For
example, such changes might not include minor adjustments like
spelling and grammatical corrections.
atom:entry elements MUST contain exactly one atom:updated element.
Publishers MAY change the value of this element over time.
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.
5.7 "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:summary element, but MUST NOT contain more than
one.
5.8 "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.
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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.
5.9 "atom:copyright" Element
The "atom:copyright" element is a Content construct that conveys a
human-readable copyright statement for the entry. atom:entry
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.
If an atom:entry element does not contain an atom:copyright element,
then the atom:copyright element of the containing atom:feed element's
atom:head element, if present, should be considered to apply to the
entry.
5.10 "atom:origin" Element
The "atom:origin" element's content conveys the original source of
the entry; e.g., the feed where the entry was first published.
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:id element in that document's atom:head section (i.e., the XPath
expression "/atom:feed/atom:head/atom:id").
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.
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6. Managing Feed State
[[ talk about what it means to keep a view of a feed ]]
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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.
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8. Embedding Atom in Other Formats
[[ ... ]]
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9. Extending Atom
[[ ... ]]
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10. IANA Considerations
An Atom Document, 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
Intended usage: COMMON
Author/Change controller: This specification's author(s). [[update
upon publication]]
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11. Security Considerations
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.
12 Normative References
[Atom-autodiscovery]
Pilgrim, M., "Atom Feed Autodiscovery", work-in-progress,
August 2004.
[Atom-protocol]
Gregorio, J. and R. Sayre, "The Atom Publishing Protocol",
work-in-progress, July 2004.
[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.
[RFC3066] Alvestrand, H., "Tags for the Identification of
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]
Wolf, M. and C. Wicksteed, "Date and Time Formats", W3C
NOTE NOTE-datetime-19980827, August 1998.
[W3C.REC-xml-20040204]
Yergeau, F., Bray, T., Paoli, J., Sperberg-McQueen, C. and
E. Maler, "Extensible Markup Language (XML) 1.0 (Third
Edition)", W3C REC REC-xml-20040204, February 2004.
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[W3C.REC-xml-infoset-20011024]
Cowan, J. and R. Tobin, "XML Information Set", W3C REC
REC-xml-infoset-20011024, October 2001.
[W3C.REC-xml-names-19990114]
Bray, T., Hollander, D. and A. Layman, "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.
[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]
[2]
Author's Address
Mark Nottingham (editor)
EMail: mnot@pobox.com
URI: http://www.mnot.net/
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Appendix A. Contributors
The following people contributed to preliminary drafts of this
document: Tim Bray, Mark Pilgrim, and Sam Ruby. The content and
concepts within are a product of the Atom community and the Atom
Publishing Format and Protocol Working Group.
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Appendix B. Revision History
[[ 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
attributes.
Clarified xml:lang inheritence.
Removed entry- and feed-specific langauge about xml:lang (covered
by general discussion of xml:lang)
Changed xml:lang to reference XML for normative requirements.
Changed "... MUST be a string" to "... is unstructued text."
Remomved langauge about DOCTYPEs, PIs, Comments, Entities.
Changed atom:url to atom:uri, @url to @uri
Introduced atom:head
Introduced "Atom Feed Document" and "Atom Entry Document".
Removed requirement for all elements and attributes to be
namespace-qualified; now children of selective elements
Added extensibility to Person constructs.
Removed requirement for media types to be registered
(non-registered media types are legal)
Added atom:origin (PaceEntryOrigin)
Added requirement for entry/id to be present and a URI
(PaceEntryIdRequired).
Clarified approach to Comments, PIs and well-formedness, as per
RFC3470.
Referenced escaping algorithm in XML.
Assorted editorial nits and cleanup, refactoring
-00: Initial IETF Internet-Draft submission.
Added optional version attribute to entry
(PaceEntryElementNeedsVersionAttribute).
Added hreflang attribute (PaceHrefLang).
Clarified inheritence of copyright element (PaceItemCopyright).
Added xml:lang to entries (PaceItemLang).
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Tweaked Infoset-related language (PaceNoInfoSet).
Clarified lack of structure in version attribute
(PaceVersionAsText).
Changed approach to XML Base (PaceXmlBaseEverywhere).
Added XML Base processing to atom:id (PaceXmlBaseId).
Various editorial cleanup and adjustments for IETF publication.
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