The WSDL (Web Services Description Language) is an XML format published for describing Web services.
WSDL is an integral part of UDDI, an XML-based worldwide business registry.
It is the language that UDDI uses.
It is an XML-based service description on how to communicate using the web service;
namely, the protocol bindings and message formats required
to interact with the web services listed in its directory.
WSDL is often used in combination with SOAP and XML Schema to provide web services over the Internet.
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.
XLang is an extension of the WSDL