Abstract: The performance of individual Web service is related to the users' locations,because service interaction messages can be easily influenced by Internet environment. As a result, service composition, which is implemented by coordinating interactions between different Web services, is also greatly impacted by Internet However, current modeling methods of service composition focus on composition itself without the impact of Internet and branch execution probability. In order to describe the relationship between service interactions, Internet environment and branch execution probability, this paper introduced a Web services performance prediction model based on generalized stochastic Petri nets. The model takes not only the situations of individual Web services but also the factors of Internet environment and branch execution probability into considerations. The model is used to evaluate and optimize the performance of service compositions.

Key words: Web service, Performance prediction model, Generalized stochastic petri nets, Performance optimization