A web service depends on three interrelated, XML-based software standards to function properly.
- Simple Object Access Protocol (SOAP)—The message format
- Web Services Description Language (WSDL)—The document that describes exactly what the web service does and how to invoke it
- Universal Discovery, Description, and Integration (UDDI)—The directory of web services that are available for use
Together, the three standards combine to give a web service the ability to function, describe itself, and be found within a network. While theoretically a web service could function fully using SOAP alone, figure 1 shows how a web service needs WSDL and UDDI to be effective.