Research On Qos-aware Dynamic Web Services Composition

From the continued evolution, Web services have become the application framework of next generation enterprise and Web systems. During the research areas of Service-Oriented Architecture, Web services have always received a lot of the concern. Nowadays, a single Web service cannot satisfy service consumers any more due to the steady increase in requirements. To solve the problem, we compose Web services from several different service providers in forms of component and specific sequence by using standard protocols, such as SOAP, WSDL and UDDI, to form a new composite service. Compared to a single Web service, a composite service is able to accomplish complex transactions and workflows which benefits from the interactions among those services. Therefore, a composite service is of high value for research and has a wide application prospect.This paper is supported by 863 program under Grant No. 2007AA01Z139,"Research on service description, selection and evaluation based on closed-loop feedback mechanism under Internet environment", and studies dynamic service composition technology all sidedly.We proposed a basic architecture of dynamic Web service composition which contains components such as: UDDI registries, Web service crawl engine, Web service repository, Web service composition engine, Web service selection engine, business rule engine, business rule repository, formula repository and the user. The architecture can successfully handle service consumers'functional requirements and pre-defined business rules to automatic compose Web services. The selection engine uses a multiobjective optimization algorithm to make decision support for the user. The nondominated sorting algorithm uses the concept of Pareto Front to represent the dominate relationship between the individuals and thus best adapt to the character of multiobjective optimization problems. The solution returns a solution set rather than a single solution, thus it helps increasing the decision level and quality.Based upon the solid research foundation, this paper implements a prototype model of QoS-based dynamic service composition. First, a great deal of experiment is executed to test and evaluate the accuracy and speed of this prototype. Results show the superiority of the NSGA-II algorithms in service composition area. Then, we analyze the distribution of Pareto solutions which can verify the main concept of our work. Finally, this paper analyzes the performance of this model and summarizes the key factors effecting accuracy and composition speed. The result of experiment has shown that this model is effective, efficient and provides a new mechanism for service composition with QoS constraints.