The Formal Study Of Services And Services Composition In Soa

Services and services composition have been a research topic for many years. Currently, there are many formal methods for services composition approaches, that from industrial standards (such as BPEL or OWL-S) to formal methods, such as Petri nets and process algebras and automata. However, these methods are not perfect, mainly because no direct message passing to describe or reasoning.In this paper, a new model is proposed, called message structure (MS), which consists of messages and message dependencies. Messages represent the incoming/outgoing data or the states of the system, and message dependencies represent activities or actions that the system might perform. MS contains five message dependencies:message creation, message termination, message choice, message synchronism and message transformation. With these, MS can model sequence, concurrency, nondeterminism choice and synchronization waiting.Service-oriented systems usually be established by messages passing, the service is by sending and receiving messages to achieve, and services composition provide services inside and outside by sending and receiving messages. In the message structure, as messages can be a variety of data sources, so message structures can be directly used to describe the services and service composition without any conversion. This paper provide the definition of services and service requestors, followed by a discussion of the service composition, and services be abstracted as the message structure model. Finally, using message structure to describe the actual service-oriented systems, and also we discussed the refining service problems. Besides, we discuss the five message dependencies corresponding code generation, and give automatic mapping transformation rules from the MS model to simple code framework.