1. A system for generating a service interface definition for a data source from an application definition, comprising: a component processor for examining a platform specific screen component and a platform neutral component forming a component based application the screen component having screen definitions to identify a screen control mapping identifying a transition between a source screen and a target screen; a service interface generation engine for generating a Web service definition for a Web service interface of a backend server of a data source, based on an operation definition describing an action supported by the data source, including: a module for constructing an outgoing message definition based on a data field in the source screen, and constructing an incoming message definition based on a data field in the target screen; and a module for constructing the operation definition having an input message and an output message, based on the identified transition, the outgoing message definition being assigned to the operation definition as the input message of the operation definition, the incoming message definition being assigned to the operation definition as the output message of the operation definition.