WSDL

WSDL (Web Services Description Language) is an XML-based language for describing web services and how to access them. A WSDL document specifies the capabilities offered by a service, the messages it can exchange, the data types involved, and the network endpoints through which the service can be invoked. While commonly used with SOAP-based services, WSDL can describe services that use other protocols as well.

A WSDL description is built around several key abstractions. The types element defines data types, typically using XML Schema. The message element defines abstract data being exchanged. The portType element groups a set of abstract operations. The binding element provides a concrete protocol and data format specification for operations defined in a portType. The service element gathers a collection of related endpoints, each represented by a port, which ties a binding to a network address.

WSDL has undergone several iterations, with WSDL 1.1 widely used in early SOAP deployments and WSDL 2.0, a later revision, offering a clarified model and improved separation of abstract definitions from concrete binding details. WSDL 2.0 can describe REST-style bindings in addition to traditional SOAP bindings.

In practice, WSDL files are often generated by service implementations or authored for interoperability. Clients use WSDL to generate code stubs or proxies, discover endpoint URLs, and determine message formats needed to invoke a service. WSDL remains a foundational technology in environments that rely on XML-based web services and contract-first service design.