The Web Services Definition/Description Language (WSDL) is an XML-based representation which provides a model to describe a web service, in this case PC*MILER Web Services. A client program connecting to a web service can read the WSDL to determine what functions are available on the server. Any special datatypes used are embedded in the WSDL file in the form of XML Schema. 

The client can then use SOAP to actually call one of the functions listed in the WSDL. Information on the WSDL can be found in the PC*MILER Web Services User’s Guide.