Dynamic Execution Strategy of Web Service Composition Based on e_SPDL and Service Container

Web service composition makes it possible for Web service reused, assembled, providing value-added service. The key problem of Web service composition is to find an effective modeling language and to describe it with composition definition language. BPEL4WS is a newly process definition language which is relatively complex and difficult to use. And BPEL4WS only supports static binding of existing services, and put binding of process and services as a known condition. But most of time dynamic service composition is needed to cater to the high dynamic environment. In this paper, firstly a process modeling language e_SPDL based on XML is proposed by simplifying and extending BPEL4WS. e_SPDL is used in the prototype system (e_Scope4WS) which supporting Web service composition. The basic structure and control structure of e_SPDL are presented in detail, and a composite service instance described in e_SPDL is given. Then the concept of service container is introduced in e_SPDL which provides the basis for dynamic service execution strategy. And the structure of service container is given. Finally the dynamic execution strategy of the process (i.e. composite service) based on e_SPDL and service container is given.