WSDL (which stands for Web Services Definition Language or Web Services Description Language) is an XML-based language for describing and locating web services. WSDL is a World Wide Web Consortium recommendation. The term WSDL is often used to mean the description of a specific web service, as in, The WSDL for that web service describes three web service methods, or referring generically to a document implemented in WSDL.
The WSDL document describes a web service using these major elements:
In the document-based pattern, WSDLs are often developed by system architects using a top-down approach, before any implementation of the service or the clients of the service. Any documents exchanged are typically designed before the WSDLs that use them. These documents are described using XML Schema, another XML-based language used to describe XML documents. The <types> section of a WSDL is actually an embedded XML Schema document. WSDL has an import capability that allows importation of externally defined XML Schema documents.