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APE (Atom/Pie/Echo) Working Group | M Nottingham
| December 2003

The Atom Syndication Format 0.3 (PRE-DRAFT)
draft-nottingham-atom-format-01

# Abstract

This specification describes version 0.3 of the Atom, an XML-based Web content and metadata syndication format.

# Editorial Notes

This draft HAS NOT been submitted for publication, and does not have any status; it should be referred to as a "pre-draft."

Discussion of this draft happens in two fora;

  The Atom Syntax mailing list
  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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# Table of Contents

1 Introduction
1.1 Conformance
1.2 Notational Conventions
2 Atom's Use of XML
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.

[[ more motivation / design principles ]]

## 1.1 Conformance

[[ talk about atom documents and atom consumers, and how requirements are placed on them ]]

## 1.2 Notational Conventions

[[ declare namespace prefixes ]]

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

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# 2 Atom's Use of XML

[[ talk about namespaces, parsing requirements, etc. / RFC 3023 / use of XML in IETF RFC / xml:base not defined for atom items / xml:lang on any element; determining precedence / namespace: http://purl.org/atom/ns# / mixed content / extensibility / serialization / what does 'contains' mean? / what does "string" mean? ]]

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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].

### 3.2.3 "atom:email" Element

The "atom:email" element's content conveys an e-mail address associated with the Person construct. Person constructs MAY contain an atom:email element, but MUST NOT contain more than one. Its content MUST be an e-mail address [RFC2822].

Ordering of the element children of Person constructs MUST NOT be considered significant.

## 3.3 Date Constructs

A Date construct is an element whose child content is a W3C Date-Time string [W3C.NOTE-datetime-19980827]. The Date-Time string's time zone SHOULD be "UTC".

## 3.4 Link Constructs

A Link construct is an element that MUST NOT have any child content, and has the following attributes:

### 3.4.1 "rel" Attribute

The "rel" attribute indicates the type of relationship that the link represents. Link constructs MUST have a rel attribute, whose value MUST be a string.

### 3.4.2 "type" Attribute

The "type" attribute indicates an advisory media type; it MAY be used as a hint to determine the type of the representation which should be returned when the URI in the href attribute is dereferenced. Note that the type attribute does not override the actual media type returned with the representation.

Link constructs MUST have a type attribute, whose value MUST be a registered media type [RFC2045].

### 3.4.3 "href" Attribute

The "href" attribute contains the link's URI. Link constructs MUST have a href attribute, whose value MUST be a URI [RFC2396].

### 3.4.4 "title" Attribute

The "title" attribute conveys human-readable information about the link. Link constructs MAY have a rel 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 [[...ref?]].

## 4.3 "atom:title" Element

The "atom:title" element is a Content construct that conveys a human-readable title for the feed. atom:feed elements MUST contain exactly one atom:title element. If the feed describes a Web resource, its content SHOULD be the same as that resource's title.

## 4.4 "atom:link" Element

The "atom:link" element is a Link construct that conveys a URI associated with the feed. The nature of the relationship as well as the link itself is determined by the element's content.

atom:feed elements MUST contain at least one atom:link element with a rel attribute value of "alternate".

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 [[what is it for?]]. atom:feed elements MAY contain [[an/one or more]] atom:info element.

## 4.12 "atom:modified" Element

The "atom:modified" element is a Date construct that indicates the time when the state of the feed was last modified, including any changes to entries therein. atom:feed elements MUST contain exactly one atom:modified element.

## 4.13 "atom:entry" Element

The "atom:entry" element's represents an individual entry that is contained by the feed. atom:feed elements MAY contain one or more atom:entry elements.

The atom:entry element MAY contain any namespace-qualified [W3C.REC-xml-names-19990114] elements as children. Ordering of the element children of atom:entry element MUST NOT be considered significant.

The following child elements are defined by this specification (note that it requires the presence of some of these elements):

### 4.13.1 "atom:title" Element

The "atom:title" element is a Content construct that conveys a human-readable title for the entry. atom:entry elements MUST have exactly one "atom:title" element. If an entry describes a Web resource, its content SHOULD be the same as that resource's title.

### 4.13.2 "atom:link" Element

The "atom:link" element is a Link construct that conveys a URI associated with the entry. The nature of the relationship as well as the link itself is determined by the element's content.

atom:entry elements MUST contain at least one atom:link element with a rel attribute value of "alternate".

atom:feed elements MUST NOT contain more than one atom:link element with a rel attribute value of "alternate" that has the same type attribute value.

atom:entry elements MAY contain additional atom:link elements beyond those described above.

### 4.13.3 "atom:author" Element

The "atom:author" element is a Person construct that indicates the default author of the entry. atom:entry elements MUST contain exactly one atom:author element, UNLESS the atom:feed element containing them contains an atom:author element itself. atom:entry elements MUST NOT contain more than one atom:author element.

[[explain inheritence]]

### 4.13.4 "atom:contributor" Element

The "atom:contributor" element is a Person construct that indicates a person or other entity who contributes to the entry. atom:entry elements MAY contain one or more atom:contributor elements.

### 4.13.5 "atom:id" Element

The "atom:id" element's content conveys a permanent, globally unique identifier for the entry. It MUST NOT change over time, even if the entry is relocated. atom:entry elements MUST contain exactly one atom:id element, whose content MUST be a URI.

### 4.13.6 "atom:modified" Element

The "atom:modified" element is a Date construct that indicates the time that the entry was last modified. atom:entry elements MAY contain an atom:modified element, but MUST NOT contain more than one.

### 4.13.7 "atom:issued" Element

The "atom:issued" element is a Date construct that indicates the time that the entry was issued.

### 4.13.8 "atom:created" Element

The "atom:created" element is a Date construct that indicates the time that the entry was created. atom:entry elements MAY contain an atom:created element, but MUST NOT contain more than one.

If atom:created is not present, its value MUST considered to be the same as that of atom:modified.

### 4.13.9 "atom:summary" Element

The "atom:summary" element is a Content construct that conveys a short summary, description or excerpt of the entry. atom:entry elements MAY contain an atom:created element, but MUST NOT contain more than one.

### 4.13.10 "atom:content" Element

The "atom:content" element is a Content construct that conveys the content of the entry. atom:entry elements MAY contain one or more atom:content elements.

If @type="multipart/alternative", @mode MUST NOT be specified, and content element MUST contain 1 or more content elements. These content elements MUST NOT specify @type="multipart/alternative" (i.e. only one level of nesting is allowed). Consumers SHOULD look at all alternative content elements and determine which one is most suitable, based on which @type and @mode the consumer supports, and preferences specified by the end user (if any). Consumers SHOULD NOT render more than one content alternative.

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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 <mnot@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.
[W3C.NOTE-datetime-19980827] | Wolf, M and Wicksteed, C, "Date and Time Formats", W3C NOTE NOTE-datetime-19980827, August 1998.
[W3C.REC-xml-names-19990114] | Bray, T, Hollander, D and Layman, A, "Namespaces in XML", W3C REC REC-xml-names-19990114, January 1999.

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# Author's Address

| Mark Nottingham
EMail: | mnot@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

2003-12-11:
  New format for atom:generator.
  New format for atom:link.
  Many elements are now Content constructs.
  Made it explicit that ordering in containers isn't significant.
  Added references.
  Added media type registration template.
  Reorganization.