Web service modeling research is largely limited to service conversation i.e. choreography. Recently, we have proposed a method to model both service orchestration and choreography using a FSM. But a flat approach (i.e. modeling at one level only) is not suitable to represent a large and complex service process. For the purpose, we propose a method to model web services using FSM modules. And shown that such a model is structured, understandable (especially while handling concurrent activities), verifiable and useful for model transformation. We have proposed two operators to model temporal behavior of web services.