[jhherren]

The first answer that comes to mind is tooling. At one extreme you have SOAP, where your IDE can make complete proxy objects from a WSDL file. At the other end is REST, where normally you're in luck if there's a nice client library to translate request/response into objects, but otherwise you're left with API documentation. (Is anyone really using WADL?) Somewhere in between is XML-RPC, where you're more than likely to find some kind of reflection method to call such as client.get_methods or something similar.

[johns]

I'm going to take this opportunity to shamelessly plug an open source project I've started for easily turning requests/responses into .NET objects: http://restsharp.org

[ramen]

There is a de-facto standard for that: system.listMethods to list supported methods, system.methodSignature to get the parameter and return types for a method, and system.methodHelp to get its documentation. It's not an ideal solution, since method signatures are shallow and not every server implements these methods the same way (or at all), but they are enough to do basic code generation for statically-typed languages. Here's an example of that for OCaml: http://code.google.com/p/xmlrpc-light/source/browse/trunk/ex...