Study On Key Technologies For Dynamic Web Services Composition With QoS Global Optimal

With the development of Internet and Web technologies, traditional distributed computing technologies have not been suitable for the Web application environment. Therefore, Web services come forth that become the focus in the area of industry and academia with the advantages, such as self-contained, modularization, loose coupling and standardization. Nowadays, compositing previous available Web services into incremental Web services with more powerful functions have been a new hotspot.However, with the prevailing of Web services, the number of services on the Internet has been larger and larger. How to select a set of services among large body of services with the same function in order to make the Composite Service achieve better performance and better quality is a hot issue in recent research. Currently, researchers of the world have made some valuable achievements on Web services composition; however, many other key technologies are to be further researched. The thesis researchs the following aspects on the basis of analyzing related status quo.Based on the studing of the difference between Web services composition and traditional workflow applications, the thesis proposes some concepts about Web services composition model and a meta-model of Web services composition process defining from two aspects, i.e. process and resource, which effectively resolves the problems on dynamic variation of Web services in composite process model.The thesis analyzes current QoS models' advantages and disadvantages, based on which proposes an objective QoS model. The model presents the relation QoS between services and ensures the composite services to implement correctly.The thesis views Web services selection problem in Web services composition as combinational optimization problem and designs QoS-globally optimal model which can satisfy the user's constrains, then presents a dynamic Web services selection approach with QoS global optimal. The approach can guarantee not only holistic optimum, but also local optimum. In order to improve the efficiency of the approach, the thesis uses Web services group concept to select candidate services.