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My gut feel is that document based web services are preferred in practice - is this other peoples experience? Are they easier to support? (I noted that SharePoint uses Any for the "document type" in its WSDL interface, I guess that makes it Document based).
Also - are people offering both WSDL and Rest type services now for the same functionality? WSDL is popular for code generation, but for front ends like PHP and Rails they seem to prefer rest.
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Document style: The SOAP Body contains one or more child elements called parts. There are no SOAP formatting rules for what the body contains; it contains whatever the sender and the receiver agrees upon. RPC style: RPC implies that SOAP body contains an element with the name of the method or operation being invoked.
WSDL allows overloaded operations. But when you add the wrapped pattern to WSDL, you require an element to have the same name as the operation, and you cannot have two elements with the same name in XML. So you must use the document/literal, non-wrapped style or one of the RPC styles.
Web Services Description Language (WSDL) is a standard specification for describing networked, XML-based services. It provides a simple way for service providers to describe the basic format of requests to their systems regardless of the underlying run-time implementation.
The document/literal encoding allows the transmission of any arbitrary valid XML document instead of a SOAP call following rules from section 5 from SOAP/1.1 specification. This allows us to send and receive SOAP packets that are more free-form ("document" style).
Document versus RPC is only a question if you are using SOAP Web Services which require a service description (WSDL). RESTful web services do not not use WSDL because the service can't be described by it, and the feeling is that REST is simpler and easier to understand. Some people have proposed WADL as a way to describe REST services.
Languages like Python, Ruby and PHP make it easier to work with REST. the WSDL is used to generate C# code (a web service proxy) that can be easily called from a static language. This happens when you add a Service Reference or Web Reference in Visual Studio.
Whether you provide SOAP or REST services depends on your user population. Whether the services are to be used over the internet or just inside your organization affects your choice. SOAP may have some features (WS-* standards) that work well for B2B or internal use, but suck for an internet service.
Document/literal versus RPC for SOAP services are described on this IBM DevelopWorks article. Document/literal is generally considered the best to use in terms of interoperability (Java to .NET etc). As to whether it is easier to support, that depends on your circumstances. My personal view is that people tend to make this stuff more complicated than it needs to be, and REST's simpler approach is superior.
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As mentioned it is better to choose the Document Literal over RPC encoded whenever possible. It is true that the old java libraries (Axis1, Glue and other prehistoric stuff) support only RPC encoded, however in today's most modern Java SOAP libs just does not support it (e.x. AXIS2, XFire, CXF). Therefore try to expose RPC encoded service only if you know that you need to deal with a consumer that can not do better. But then again maybe just XML RPC could help for these legacy implementations.
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