Choreography And Orchestration Conformance For System Design

Orchestration and Choreography are two languages commonly used for describing web services composition. The differences between orchestration and choreography are the former one is a peer to peer model and in a business process there are many coordinators; the later one is a hierarchical requester/provider model. Choreography defines the cooperations from a top view manner, while orchestration defines when and how to invoke a service from one point of view. According to their characteristics, we could use choreography to describe the protocol on the higher level and the other one for defining the action of every single service. This approach has two advantages: firstly, it provides a top-down way for system design; secondly, it supports the comformance verification.This kind of designing method needs a formal system which could describe choreography and orchestration. This paper analyses the advantages and disadvantages of different formal methods, and uses algebra process to formally describe the composition system. Through the analysis of a theroy service composition, we concluded the disadvantages of current system solution. For these disadvantages, we added the description of status, enhancing the expressive ability, and make them have the capability to describe choice, switch and other kind of structure. We define a three layered system which are inter-process, between-process and between service, layered the cooperation semantics for designing a system in different layer. Because the compostion system is uncertain, in the paper, we impliment system status mobility, location mobility, interface mobility and function mobility, using some examples to explain that. Meanwhile we give the method to change from orhestration system to BPEL language, which will be a great help for automatical creation of codes.In the end of the paper, we give an example of a airway plane ticket selling system. We design the choreography and orchestration description. According to the system comformance, we analyse a fault orchestration design and then give a right and refined one. The mapping of the whole formal system to BPEL is also provided.