RSS (most commonly translated as "Really Simple Syndication" but sometimes "Rich Site Summary") is a family of web feed formats used to publish frequently updated works—such as blog entries, news headlines, audio, and video—in a standardized format.
An RSS document (which is called a "feed", "web feed", or "channel") includes full or summarized text, plus metadata such as publishing dates and authorship. Web feeds benefit publishers by letting them syndicate content automatically.
They benefit readers who want to subscribe to timely updates from favored websites or to aggregate feeds from many sites into one place.
RSS feeds can be read using software called an "RSS reader", "feed reader", or "aggregator", which can be web-based, desktop-based, or mobile-device-based. A standardized XML file format allows the information to be published once and viewed by many different programs. The user subscribes to a feed by entering into the reader the feed's URI or by clicking an RSS icon in a web browser that initiates the subscription process. The RSS reader checks the user's subscribed feeds regularly for new work, downloads any updates that it finds, and provides a user interface to monitor and read the feeds.
RSS formats are specified using XML, a generic specification for the creation of data formats.
Although RSS formats have evolved from as early as March 1999, it was between 2005 and 2006 when RSS gained widespread use, and the icon was decided upon by several major Web browsers.
There are several different versions of RSS, falling into two major branches (RDF and 2.).
The RDF (or RSS 1.*) branch includes the following versions:
RSS 0.90 was the original Netscape RSS version. This RSS was called RDF Site Summary, but was based on an early working draft of the RDF standard, and was not compatible with the final RDF Recommendation.
RSS 1.0 is an open format by the RSS-DEV Working Group, again standing for RDF Site Summary.
RSS 1.0 is an RDF format like RSS 0.90, but not fully compatible with it, since 1.0 is based on the final RDF 1.0 Recommendation.
RSS 1.1 is also an open format and is intended to update and replace RSS 1.0. The specification is an independent draft not supported or endorsed in any way by the RSS-Dev Working Group or any other organization.
The RSS 2. branch (initially UserLand, now Harvard) includes the following versions:
RSS 0.91 is the simplified RSS version released by Netscape, and also the version number of the simplified version originally championed by Dave Winer from Userland Software. The Netscape version was now called Rich Site Summary; this was no longer an RDF format, but was relatively easy to use.
RSS 0.92 through 0.94 are expansions of the RSS 0.91 format, which are mostly compatible with each other and with Winer's version of RSS 0.91, but are not compatible with RSS 0.90.
RSS 2.0.1 has the internal version number 2.0. RSS 2.0.1 was proclaimed to be "frozen", but still updated shortly after release without changing the version number. RSS now stood for Really Simple Syndication. The major change in this version is an explicit extension mechanism using XML namespaces.
For the most part, later versions in each branch are backward-compatible with earlier versions (aside from non-conformant RDF syntax in 0.90), and both versions include properly documented extension mechanisms using XML Namespaces, either directly (in the 2.* branch) or through RDF (in the 1.* branch). Most syndication software supports both branches. "The Myth of RSS Compatibility", an article written in 2004 by RSS critic and Atom advocate Mark Pilgrim, discusses RSS version compatibility issues in more detail.
The extension mechanisms make it possible for each branch to track innovations in the other. For example, the RSS 2.* branch was the first to support enclosures, making it the current leading choice for podcasting, and as of 2005[update] is the format supported for that use by iTunes and other podcasting software; however, an enclosure extension is now available for the RSS 1.* branch, mod_enclosure. Likewise, the RSS 2.* core specification does not support providing full-text in addition to a synopsis, but the RSS 1.* markup can be (and often is) used as an extension.
There are also several common outside extension packages available, including a new proposal from Microsoft for use in Internet Explorer.
The most serious compatibility problem is with HTML markup. Userland's RSS reader—generally considered as the reference implementation—did not originally filter out HTML markup from feeds. As a result, publishers began placing HTML markup into the titles and descriptions of items in their RSS feeds. This behavior has become expected of readers, to the point of becoming a de facto standard, though there is still some inconsistency in how software handles this markup, particularly in titles. The RSS 2.0 specification was later updated to include examples of entity-encoded HTML; however, all prior plain text usages remain valid.
As of January 2007, tracking data from www.syndic8.com indicates that the three main versions of RSS in current use are 0.91, 1.0, and 2.0. Of these, RSS 0.91 accounts for 13 percent of worldwide RSS usage and RSS 2.0 for 67 percent, while RSS 1.0 has a 17 percent share. These figures, however, do not include usage of the rival web feed format Atom. As of August 2008[update], the syndic8.com website is indexing 546,069 total feeds, of which 86,496 were some dialect of Atom and 438,102 were some dialect of RSS.
The primary objective of all RSS modules is to extend the basic XML schema established for more robust syndication of content. This inherently allows for more diverse, yet standardized, transactions without modifying the core RSS specification.
To accomplish this extension, a tightly controlled vocabulary (in the RSS world, "module"; in the XML world, "schema") is declared through an XML namespace to give names to concepts and relationships between those concepts.
Some RSS 2.0 modules with established namespaces are:
Ecommerce RSS 2.0 Module
Media RSS 2.0 Module
OpenSearch RSS 2.0 Module
Confusion between Web feed and RSS
The term RSS is often used to refer to web feeds or web syndication in general, although not all feed formats are now RSS. The Blogspace description of using web feeds in an aggregator, for example, is headlined "RSS info" and "RSS readers" even though its first sentence makes clear the inclusion of the Atom format: "RSS and Atom files provide news updates from a website in a simple form for your computer.
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