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The name Atom applies to a pair of related standards. The Atom
Syndication Format is an
XML language used for
while the Atom Publishing Protocol (APP is the acronym, but it is
referred to as 'AtomPub' for short) is a simple HTTP-based protocol
for creating and updating Web resources.
Web feeds allow
programs to check for updates published on a web site. To provide a web feed, a
site owner may use specialized software (such as a
content management system) that publishes a list (or "feed") of recent
articles or content in a standardized, machine-readable format. The feed can
then be downloaded by web sites that syndicate content from the feed, or by
reader programs that allow Internet users to subscribe to feeds and view
A feed contains entries, which may be headlines, full-text articles,
excerpts, summaries, and/or links to content on a web site, along with various
The development of Atom was motivated by the existence of many incompatible
versions of the
RSS syndication format, all of which had shortcomings, and the poor
 of XML-RPC-based publishing protocols. The Atom syndication format was
published as an IETF "proposed
RFC 4287. The Atom Publishing Protocol is still in draft form.
Web feeds are used by the
community to share the latest entries' headlines or their full text, and even
attached multimedia files. (See
vodcasting, broadcasting, screencasting, Vloging, and MP3 blogs.)
These providers allow other websites to incorporate the weblog's "syndicated"
headline or headline-and-short-summary feeds under various usage agreements.
Atom and other web syndication formats are now used for many purposes, including
journalism, marketing, bug-reports, or any other activity involving periodic
updates or publications. Atom also provides a standardized way to export an
entire blog, or parts of it, for backup or for importing into other blogging
A program known as a
feed reader or aggregator can check webpages on behalf of a user and display any
updated articles that it finds. It is common to find web feeds on major Web
sites, as well as many smaller ones. Some websites let people choose between RSS
or Atom formatted web feeds; others offer only RSS or only Atom. In particular,
many blog and
wiki sites offer
their web feeds in the Atom format.
Client-side readers and aggregators may be designed as standalone programs or
as extensions to existing programs like web browsers. Browsers are moving toward
integrated feed reader functions, such as Safari RSS, Web Browser for S60,
Opera, Firefox and Internet Explorer. Such programs are available for various operating
Web-based feed readers and news aggregators require no software installation
and make the user's "feeds" available on any computer with Web access. Some
aggregators syndicate (combine) web feeds into new feeds, e.g., taking all
football related items from several sports feeds and providing a new football
feed. There are also search engines for content published via web feeds,
including Technorati and Blogdigger.
On Web pages, web feeds (Atom or RSS) are typically linked with the word
"Subscribe" or with the unofficial web feed logo.
Atom Compared to RSS 2.0
The main motivation for the development of Atom was dissatisfaction with
. Among other things, there are multiple incompatible and widely adopted
versions of RSS. The intention was to ease the difficulty of developing
applications with web syndication feeds.
A brief description of the ways Atom 1.0 seeks to differentiate itself from
RSS 2.0 follows
- RSS 2.0 may contain either plain text or escaped HTML as a payload, with
no way to indicate which of the two is provided. Atom in contrast uses an
explicitly labeled (i.e. typed) "entry" (payload) container. It allows for a
wider variety of payload types including plain text, escaped HTML, XHTML,
binary, and references to external content such as documents, video and
audio streams, and so forth.
- RSS 2.0 has a "description" element which can contain either a full
entry or just a description. Atom has separate “summary” and “content”
elements. Atom thus allows the inclusion of non-textual content that can be
described by the summary.
- Atom is defined within an
XML namespace whereas RSS 2.0 is not.
- Atom specifies use of the XML's built-in xml:base for relative
URIs. RSS 2.0 does not have a means of differentiating between relative
and non-relative URIs.
- Atom uses XML's built-in xml:lang attribute as opposed to RSS 2.0's use
of its own "language" element.
- In Atom, it is mandatory that each entry have a
globally unique ID, which is important for reliable updating of entries.
- Atom 1.0 allows standalone Atom Entry documents whereas with RSS 2.0
only full feed documents are supported.
- Atom specifies that dates be in the format described in
RFC 3339 (which is a subset of
The date format in RSS 2.0 was underspecified and has led to many different
formats being used.
- Atom 1.0 has
IANA-registered MIME-type. RSS 2.0 feeds are often sent as application/rss+xml,
although it is not a registered MIME-type.
Atom 1.0 includes an XML schema. RSS 2.0 does not.
- Atom is an open and evolvable standard developed through the
standardization process. RSS 2.0 is not standardized by any standards body.
Furthermore according to its copyright it may not be modified.
- Atom 1.0 elements can be used as extensions to other XML vocabularies,
including RSS 2.0 as illustrated in a
by Tim Bray entitled
- Atom 1.0 describes how feeds and entries may be digitally signed using
XML Digital Signature specification such that entries can be copied
across multiple Feed Documents without breaking the signature.
- Despite the emergence of Atom as an IETF Proposed Standard and the
decision by major companies such as Google to
embrace Atom, use of the older and more widely known RSS 1.0 and RSS 2.0
formats has continued.
- RSS 2.0 support for enclosures led directly to the development of
While many podcasting applications, such as iTunes,
support the use of Atom 1.0, RSS 2.0 remains the preferred format
- Many sites choose to publish their feeds in only a single format. For
example CNN, the New York Times, and the BBC offer their
web feeds only in RSS 2.0 format.
- News articles about web syndication feeds have increasingly used the
term "RSS" to refer generically to any of the several variants of the RSS
format such as RSS 2.0 and RSS 1.0 as well as the Atom format. (For example,
"Fine-Tuning Your Filter for Online Information" (NYT) and
"There's a Popular New Code for Deals: RSS" (NYT January 29, 2006))
- Each of the various web syndication feed formats has attracted large
groups of supporters who remain satisfied by the specification and
capabilities of their respective formats.
Before the creation of Atom the primary method of web content syndication was
RSS family of formats.
Members of the community who felt there were significant deficiencies with
this family of formats were unable to make changes directly to RSS 2.0 because
the official specification document stated that it was purposely frozen to
ensure its stability.
In June 2003, Sam Ruby set up a wiki
to discuss what makes
"a well-formed log entry". This initial posting acted as a rallying point.
 People quickly started using the wiki to discuss a new syndication
format to address the shortcomings of
RSS. It also became clear that the new format could also form the basis of a
more robust replacement for blog editing protocols such as Blogger API and
LiveJournal XML-RPC Client/Server Protocol.
The project aimed to develop a web syndication format that was:
- "100% vendor neutral,"
- "implemented by everybody,"
- "freely extensible by anybody, and"
- "cleanly and thoroughly specified."
In short order, a
project road map was built. The effort quickly attracted
more than 150 supporters including
David Sifry of Technorati, Mena Trott of Six Apart, Brad Fitzpatrick of
LiveJournal, Jason Shellen of Blogger, Jeremy Zawodny of Yahoo, Timothy Appnel
of the O'Reilly Network, Glenn Otis Brown of Creative Commons and Lawrence
Lessig. Other notables supporting Atom include Mark Pilgrim, Tim Bray, Aaron
Swartz, Joi Ito, and Jack Park.
the key figure behind
RSS 2.0, gave tentative support to the Atom endeavor (which at the time was
After this point, discussion became chaotic, due to the lack of a
decision-making process. The project also lacked a name, tentatively using
"Pie," "Echo," and "Necho" before settling on Atom. After releasing a project
snapshot known as Atom 0.2 in early July 2003, discussion was shifted off
Atom 0.3 and Adoption by Google
The discussion then moved to a newly set up mailing list. The next and final
snapshot during this phase was Atom 0.3, released in December 2003. This
version gained widespread adoption in syndication tools, and in particular it
was added to several Google-related services, such as Blogger, Google News, and
Gmail. Google's Data APIs (Beta) GData are based
on Atom 1.0 and RSS 2.0.
Atom 1.0 and IETF Standardization
In 2004, discussions began about moving the project to a standards body such
as the World Wide Web Consortium or the Internet Engineering Task Force (IETF).
The group eventually chose the IETF and the Atompub working group was formally
set up in June 2004, finally giving the project a charter and process. The
Atompub working group is co-chaired by Tim Bray (the co-editor of the XML specification)
and Paul Hoffman. Initial development was focused on the syndication format.
The Atom Syndication Format was issued as a Proposed Standard in IETF
RFC 4287 in December 2005. The co-editors were
Mark Nottingham and Robert Sayre.
This document is known as 'atompub-format' in IETF's terminology. As of May,
2007 three other drafts were still being worked on as part of the IETF process.
They are atompub-protocol, atompub-typeparam and atompub-autodiscovery. Their
contents and current status can be viewed at
IETF's web site.
Example of an Atom 1.0 Feed
An example of a document in the Atom Syndication Format:
<?xml version="1.0" encoding="utf-8"?>
<link href="http://example.org/feed/" rel="self"/>
<title>Atom-Powered Robots Run Amok</title>
- Atom standard
- Atom advocacy / evangelism:
- Atom history & motivation
- Atom working group links
- Atom Extension Standards
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