New from PHPBuilder.com today there's an article from Curtis Dicken introducing web services, specifically SOAP-based ones, in PHP applications.

Today, whether you realize it or not, websites all around the world use web services to distribute and receive data. In this article we will take a look at what web services are and the basic concepts on how they are implemented and used.

He starts with the basics - XML and how messages are structured, then on to the SOAP format and an example of a simple message sending domain name information to the remote server. He briefly covers WSDL files (the description for the web service's functionality) and UDDI (Universal Description, Discovery and Integration), a structure to provide a directory of SOAP services for developers to choose from.