WSDL

WSDL
Web Service Description Language (WSDL) is an XML document standard defined to describe a SOAP web service. Specifically, a WSDL defines the message, portType, binding and services of a Web Service. The message is basically the XML schema of the SOAP envelope contents, including message structure and the data types used in the message. The portType describes groups of operations (methods) including input and output messages (parameters). The binding describes the specifics of a portType, including style and soapAction. Finally, the service section describes the location of the Web Service, which is often a URL.

WSDLs are consumed by programs which create proxy classes such as wsdltojava from Apache Axis, which generates Java, or wsdl.exe in .NET, which generates VB, C#, or JS. WSDLs are also consumed by Web Service messaging products such as XML Spy Pro and Microsoft InfoPath.

WSDLs are created from classes by javatowsdl or directly by Web Service servers. IIS automatically produces a WSDL for a .NET Web Service. Axis will produce a WSDL from a jws file, which I will discuss next week.

What this means to the enterprise
Simply wrapping a legacy application in a Web Service is very powerfull. This allows Web Service enabled application, such as Microsoft Office, to talk to the Applications (more easily). The preliminary schema validation of the message occurred client side, with no additional programming. This validation, combined with the definition of a specific message description in the WSDL, including readable legacy field names with some meaning, enabled a user, to build an application that consumed this web service.

References

• http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnwebsrv/html/understandwsdl.asp
• http://radio.weblogs.com/0101679/stories/2002/02/15/aBusyDevelopersGuideToWsdl11.html
• http://ws.apache.org/axis/java/integration-guide.html