An aggregator or news aggregator or feed reader is a client software that uses web feed to retrieve syndicated web content such as blogs, podcasts, vlogs, and mainstream mass media websites, or in the case of a search aggregator, a customized set of search results.
Aggregators reduce the time and effort needed to regularly check websites for updates, creating a unique information space or "personal newspaper." Once subscribed to a feed, an aggregator is able to check for new content at user-determined intervals and retrieve the update. 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 being built into portal sites such as My Yahoo! and Google; modern web browsers; and e-mail programs.
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, news readers or search aggregators.
The syndicated content an aggregator will retrieve and interpret is usually supplied in the form of RSS or other XML-formatted data, such as RDF/XML or Atom.
 Online version
Online versions of this type of software are websites selling or providing aggregation services for free; these sites are typically provided by ISPs and internet portals. The RSS feeds allow users to check recently changed versions in comparison to previous updates. This allows only 'fresh data' to be viewed, reducing bandwidth demands on the provider's hardware and users. Because the aggregator is online, it can be accessed anywhere by any user who is connected to the internet. More advanced ways of integrating feeds are provided by Ajax desktops, which allow users to aggregate OPML files, email services and documents in Google Docs & Spreadsheets as well as feeds in a single interface.
Lately, a large number of online news aggregators made their way on our Internet search results. The success of the technology comes from two perspectives:
- first - a large amount of online content can be put together in a short period of time, optimising sites for organic search engine listings;
- second – the advertising capabilities can be enormous as the ad content can be delivered more targeted and “by the second”.
 Computer version
The desktop version of this type of software is designed to satisfy the task of controlling subscriptions and supervising the RSS feeds that the user has selected. The GUI of this type of software is normally a three-panel composition similar to most e-mail clients, but browser versions are available and normally run on a LAN. Content is published through web-servers so that global access is possible. Additional facilities may be integrated into aggregators, such as audio players, blog editors, internet browsers and e-mail clients.
 Keyword Filtering
One of the problems with news aggregators is that the volume of articles can sometimes be overwhelming, especially when the user has many feeds. A process called Keyword Filtering can be used to actively include (or discard) articles if they contain certain keywords that the user has defined. For example, if the user is interested in gaming, then the keywords Playstation, Nintendo and Xbox can be used to include relevant articles.
A small number of news aggregators have the ability to register to clouds, a web service that notifies the aggregator of updates to a feed, eliminating the need for periodic pulling. This approach attempts to produce a more efficient use of bandwidth, though the overhead associated with registering a cloud can mean no net savings. 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.
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