For a web page to access and use a web service, it must communicate with the service and have a description of the functionality the service provides, the available methods that it can invoke, and the parameters the service returns. The Web Service Description Language (WSDL) is an XML-based description of the service. Each web service provides a WSDL that describes how to bind to the service, the available methods that the web page can invoke, and the data inputs and outputs. The WSDL can reside in a file, or it can be generated by the web service at runtime.

Communication between the web page requesting the service and the web service itself uses the Simple Object Access Protocol (SOAP). SOAP is an XML-based protocol that lets a web client access and invoke the web service’s methods and parameters.