RESTful Clients and WADL Documents

At the core of a SOAP-based service is the service contract, a WSDL document. WSDL is an XML dialect. In modern web services, the WSDL plays the role that the IDL document plays in the DCE/RPC services introduced in Chapter 1. In any case, the WSDL document has various sections, all of which are required except for the types section that contains an XML Schema or equivalent; modern WSDLs almost always include a schema. The information in the WSDL specifies the invocation syntax for every operation encapsulated in the service. SOAP frameworks such as Java Metro and DotNet provide tools that, given a WSDL, can generate client-side library code, which facilitates the programming of a client against the service. The WSDL itself is language-neutral, and the publisher of the service typically generates at least the first draft of this service contract, which can then be refined as needed. In principle, a WSDL document could describe either a SOAP-based or a REST-style service; in practice, however, the WSDL is used predominantly for SOAP-based services. Chapter 4, which introduces SOAP-based examples, looks closely at the WSDL document. For now, the similarity between a WSDL document and a WADL (Web Application Description Language) document is of interest.

As noted, WSDL documents can describe either category of web service, SOAP-based or REST-style, but there seems to be little interest in WSDLs and WSDL-based tools for RESTful services. JAX-RS implementations ...

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