Web Service Styles of Use
Web services are a set of tools that can be used in a number of ways. The three most common styles of use are RPC, SOA and REST.
Remote procedure calls
RPC Web services present a distributed function (or method) call interface that is familiar to many developers. Typically, the basic unit of RPC Web services is the WSDL operation.
The first Web services tools were focused on RPC, and as a result this style is widely deployed and supported. However, it is sometimes criticised for not being loosely coupled, because it was often implemented by mapping services directly to language-specific function or method calls… Many vendors felt this approach to be a dead end, and pushed for RPC to be disallowed in the WS-I Basic Profile.
Service-oriented architecture
Web services can also be used to implement an architecture according to Service-oriented architecture (SOA) concepts, where the basic unit of communication is a message, rather than an operation. This is often referred to as “message-oriented” services.
SOA Web services are supported by most major software vendors and industry analysts. Unlike RPC Web services, loose coupling is more likely, because the focus is on the “contract” that WSDL provides, rather than the underlying implementation details.
Representational state transfer
Finally, RESTful Web services attempt to emulate HTTP and similar protocols by constraining the interface to a set of well-known, standard operations (e.g., GET, PUT, DELETE). Here, the focus is on interacting with stateful resources, rather than messages or operations.
RESTful Web services can use WSDL to describe SOAP messaging over HTTP, which defines the operations, or can be implemented as an abstraction purely on top of SOAP (e.g., WS-Transfer).
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