WSDL / SOAP
The Web Services Description Language (WSDL) is the historical XML-based interface definition language for SOAP web services. WSDL 1.1 (2001) is the most widely deployed version; WSDL 2.0 is a W3C Recommendation (2007). SOAP and WSDL are governed by the W3C and remain critical in legacy enterprise and government integrations. Documented here as the historical baseline for service interface specifications.