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Atom

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Atom
File extension:	.atom, .xml
MIME type:	application/atom+xml
Type of format:	Syndication
Extended from:	XML

The name Atom applies to a pair of related standards. The Atom Syndication Format is an XML language used for web feeds, 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 software 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 feed reader programs that allow Internet users to subscribe to feeds and view their content.

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 metadata.

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 interoperability [1] of XML-RPC-based publishing protocols. The Atom syndication format was published as an IETF "proposed standard" in RFC 4287. The Atom Publishing Protocol is still in draft form.

Usage

Web feeds are used by the weblog community to share the latest entries' headlines or their full text, and even attached multimedia files. (See podcasting, 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 systems.

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 systems.

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 RSS [2]. 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 [3], [4]:

• 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, XML, Base64-encoded 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
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