Content Syndication with RSS

Tools for Processing XML

While RSS can be parsed directly using text-processing tools, XML parsers are often more convenient. Many parsers exist for using XML with many different programming languages. Most are freely available, and the majority are open source.

Selecting a Parser

An XML parser typically takes the form of a library of code that you interface with your own program. The RSS program hands the XML over to the parser, and the parser hands back information about the contents of the XML document. Typically, parsers do this either via events or via a document object model.

With event-based parsing, the parser calls a function in your program whenever a parse event is encountered. Parse events include things like finding the start of an element, the end of an element, or a comment. Most Java event-based parsers follow a standard API called SAX, which is also implemented for other languages such as Python and Perl. You can find more about SAX at http://www.saxproject.org.

Document object model (DOM)-based parsers work in a markedly different way. They consume the entire XML input document and hand back a tree-like data structure that the RSS software can interrogate and alter. The DOM is a W3C standard; documentation is available at http://www.w3.org/DOM.

Choosing whether to use an event- or DOM-based model depends on the application. If you have a large or unpredictable document size, it is better to use event-based parsing for reasons of speed and memory consumption (DOM ...