to my knowledge, both use xml over http in the form of
soap messages but the difference is to what level of xml detail in the soap message. for rpc, the xml has information of the calling method, arguments, return values and no information of how complex types if any are transferred over the wire unlike document type where there the actual soap message has information of how the complex types are transferred.
and people (WS-I Basic Profile) say that using rpc/encoded style web services we cannot achive interopability which can be achieved by document/literal style and rpc/literal style web services.
can anyone please correct me ...