REST, RPC, and SOAP you have their guiding principles of what they're trying to accomplish and how they're trying to go?? about it so, if you're designing your API you should ideally work with the guiding principles of the system you're using to provide your API so, if you look at RPC in this case, XML-RPC it's actually the guiding principle is right there is the name so, you're doing a Remote Procedure Call it's a way of exposing functions, or methods, over the Web, so you're able to call them remotely and get some data back very much like procedures in structured programming instead of having to functions memomy there are in servers across the world and so, the first professionnal job I ever took had a very explicit XML-RPC API and in a certain sense, it was great ! you know, this is very simple to understand callign methods, this is something that we all do, every day, as developers and so, you know, make it over the Web, sounds about right ! there is some things that eventually break down ????? so that's XML-RPC, and the reason you'd build something that way or it's guiding priciple 