PHPMaster.com: Creating Web Services with PHP and SOAP, Part 1
In this first of a two part series on web services I'll talk about the SOAP specification and what is involved in creating SOAP messages. I'll also demonstrate how to create a SOAP server and client using the excellent NuSOAP library to illustrate the flow of SOAP. In the second part I'll talk about the importance of WSDL files, how you can easily generate them with NuSOAP as well, and how a client may use a WSDL file to better understand your web service.
He introduces you to the concepts behind SOAP, the normal structure of a SOAP-formatted XML message and what an example might look like for fetching a stock price from a remote service. He then shows how to use NuSOAP to create both a simple server and client to pull information about books - sample code and a screenshot of the output is included.