What are Feeds?

You can think of feeds as small modules of information that can be plugged into existing websites, consumed by clients on their desktop, or consumed by aggregators to be presented by users with other feeds. Aggregators also offer searching functionality to users, allowing new users to locate your site and feed (a great reason to provide a feed in the first place).

• Websites such as Yahoo! produce web feeds.

• Software that downloads and uses feeds is said to consume or aggregate feeds.

• Sites such as Google News that retrieve feeds from a number of sources and display selected items are called aggregators.

Figure 2-1 shows feeds in action.

Figure 2-1

Most feeds are provided in one of two formats, either RSS (Rich Site Summary, or RDF Site Summary, depending on who you ask) or Atom. These formats provide standardized ways for information to be presented, such as templates for the content providers to stick their information into. The use of these standard display formats by different (and otherwise competing) websites has been a major component of the success of feeds, because a piece of software need only be written once, and it can consume the relevant information from a wide variety of different sites.

RSS

RSS is likely the more prevalent format on the Web. It was originally developed by Netscape to give content providers an easy way to have their information plugged into their My Netscape portal (a user-configurable homepage that contains news sources selected by the user). Further versions were developed by others until the 2.0 specification was released and declared to be the final version in the series. Most sites using RSS either provide a feed in 0.91 or 2.0 — I have yet to find a site only providing a feed in the 1.0 version of the spec. The full specification for all three versions is available in Appendix B.

Atom

Atom was developed after RSS to resolve perceived failings of the now complete RSS specification. It makes more extensive use of namespacing for all of its elements, and currently sits at predraft status for its 0.3 state, where it has sat since late 2003. Despite all the warnings in the specification about not using it until it is officially released, most sites and aggregators offering Atom support make use of the 0.3 version of the spec. You can find the 0.3 version of the specification in Appendix B.