The Research For QoS Driven Service Composition

Web service is an application program, which is based on internet, distributed, self-included, self-described and modular. More and more enterprises are publishing then-application programs as Web services. Accordingly, the service users' demands of the response speed, service functions and service quality are becoming higher and higher. And single services from suppliers are becoming hard to meet the demands of the users. So, it's natural for the emergence of composition services.Service composition is to combine the relative services dynamically in term of situation requires, and publish a new service which can implement particular tasks. From the aspect of application, composition of services can realize software and hardware share of the virtual community;from the service itself, composition of the services realizes dynamic production of the composed services, which not only saves the development cost of the services, but improves reusability and utilization ratio of the service components.One of the most challenging problems of the service composition is service quality. Its purpose is to find a group of optimal services under users' constrains, from which a new service is combined and the best service quality is assured.The thesis mainly discusses the design and implementation of the service composition system.First, a system of service composition based on QoS is put forward, which includes the architecture and the work flow.Second, the thesis designs the QoS model of the system, which includes the QoS attributes of single service and the QoS computation of composite service.Finally, the thesis designs the approach of service composition based on genetic algorithm. Its performances are evaluated by some experiments. Then, the approach is applied to the system.