An aggregator or news aggregator is a type of software that retrieves syndicated Web content that is supplied in the form of a web feed (RSS, Atom and other XML formats), and that are published by weblogs, podcasts, vlogs, and mainstream mass media websites.
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Aggregators reduce the time and effort needed to regularly check websites of interest for updates, creating a unique information space or "personal newspaper." An aggregator is able to subscribe to a feed, check for new content at user-determined intervals, and retrieve the content. The content is sometimes described as being "pulled" to the subscriber, as opposed to "pushed" with email or IM. Unlike recipients of some "pushed" information, the aggregator user can easily unsubscribe from a feed.
Aggregator features are gradually being built into portal sites such as My Yahoo! and Google, Web browsers such as Mozilla Firefox, Safari, Opera, e-mail programs like Microsoft Outlook, and other applications, including Apple's iTunes, which serves as a podcast aggregator.
The aggregator provides a consolidated view of the content in a single browser display or desktop application. Such applications are also referred to as RSS readers, feed readers, feed aggregators or news readers, although in Internet communication, the latter term was first used for programs that read Usenet newsgroups.
A website may incorporate aggregator features by republishing syndicated content on one or more of its pages. Aggregator features also may be incorporated in other client software, including Web browsers, e-mail clients, weblog creation programs, or media player programs. Devices such as mobile phones or Tivo video recorders (already aggregating television programs) may incorporate XML aggregators.
The syndicated content an aggregator will retrieve and interpret is usually supplied in the form of RSS or other XML-based data, such as RDF or Atom formats.
Some news aggregators have the ability to register to clouds, centralized folksonomic services that monitor and track many syndicated content sources online. An aggregator using a cloud will receive notifications from the cloud server only when there are updates, thus eliminating the need for periodic polling. This approach attempts to produce a more efficient use of bandwidth, though the overhead associated with registering a cloud can mean no net saving. It also introduces issues of scalability and a single point of failure among others. In the time since the cloud concept was introduced in 2000, very few sources have implemented it.
Desktop aggregators are software applications that are dedicated to the task of managing the subscriptions, monitoring and syndicated content of a user. Many aggregators display content in a window or list view similar to any email-program.
Other desktop aggregators have browser-based interfaces that look and operate like a Web-based aggregator, but are typically run on a local system and administered by the user. The interface may be served through an integrated HTTP server, that can be accessed from anywhere once the user's network is properly configured.
Some desktop applications may have aggregator functionality in addition to their primary function, such as a web browser, email client, music player or weblog editor.
An online aggregator is a website service offering aggregator functionality, typically hosted by a service provider or portal site. Feeds are checked for updates by the service, thus reducing the bandwidth that multiple desktop aggregators would consume polling feeds individually. Since they are remotely hosted, online aggregators are accessible from anywhere, but are only as reliable as the service provider. These aggregators can be free or commercial. Web-based aggregators of blogs which are related to some project or group are often called "planets", named after the program Planet used to generate them.
Providers of aggregation services to news portals and search engines (not necessarily direct to end users).