In Codewalkers.com's latest piece, the author dives into the topic of XML-RPC with PHP through the PEAR::XML-RPC library.

Remote procedure calls enable developers to create distributed applications. Various program components, perhaps some of which may be considered programs in their own right, reside on separate host machines but all work together to form a complete application. The call one component makes to another on a separate host is a remote procedure call (RPC).

Not only is XML-RPC a great way to pass standard information back and forth, it's also a clean, simple way to share (and control) access to data from the outside. Whole APIs have been developed using this technology, making it a simple matter to whip up your own. The author goes through everything you'll need to get started, including some sample functionality, a complete description of that code, and how the client and server work together.