The ability to efficient selection and integration of inter-organizational heterogeneous Web services at runtime becomes an important requirement to the Web service provision. In an Web service application, if no single existing Web service can satisfy the functionality required by the user, there should be a program or an agent to automated combine existing services together in order to fulfill the request.
The aim of this thesis is to consider the Web service composition problem from the viewpoint of logic-based program synthesis, and to propose an agent-based framework for supporting the composition process in scalable and flexible manner. The approach described in this thesis uses Linear Logic-based theorem proving to assist and automate composition of Semantic Web services. The approach uses a Semantic Web service language (DAML-S) for external presentation of Web services, while, internally, the services are presented by extralogical axioms and proofs in Linear Logic. Linear Logic, as a resource conscious logic, enables us to capture the concurrent features of Web services formally (including parameters, states and non-functional attributes). The approach uses a process calculus to present the process model of the composite service. The process calculus is attached to the Linear Logic inference rules in the style of type theory. Thus the process model for a composite service can be generated directly from the complete proof. We introduce a set of subtyping rules that defines a valid dataflow for composite services.
The subtyping rules that are used for semantic reasoning are presented with Linear Logic inference figures. The composition system has been implemented based on a multi-agent architecture, AGORA. The agent-based design enables the different components for Web service composition system, such as the theorem prover, semantic reasoner and translator to integrated to each other in a loosely coupled manner.
We conclude with discussing how this approach has been directed to meet the main challenges in Web service composition. First, it is autonomous so that the users do not required to analyze the huge amount of available services manually. Second, it has good scalability and flexibility so that the composition is better performed in a dynamic environment. Third, it solves the heterogeneous problem because the Semantic Web information is used for matching and composing Web services.
We argue that LL theorem proving, combined with semantic reasoning offers a practical approach to the success to the composition of Web services. LL, as a logic for specifying concurrent programming, provides higher expressive powers in the modeling of Web services than classical logic. Further, the agent-based design enables the different components for Web service composition system to integrated to each other in a loosely coupled manner.
The main contributions of this thesis is summarized as follows. First, an generic framework is developed for the purpose of presenting an abstract process of the automated Semantic Web service composition. Second, a specific system based on the generic platform has been developed. The system focuses on the translation between the internal and external languages together with the process extraction from the proof. Third, applications of the subtyping inference rules that are used for semantic reasoning is discussed. Fourth, an agent architecture is developed as the platform for Web service provision and composition.