Composition and Reduction of Web Service Based on Dynamic Timed Colored Petri Nets

An application system for enterprises is a composite Web service that consists of a collection of Web services related by data and control flow. It’s necessary to get formalizing and modeling techniques and graphic tools for reliable Web Service and its application construction. In this paper we present the formalization of Web services and the algorithm for constructing composition. Firstly, we propose a dynamic timed colored Petri net (DTCPN) to model and analyze a Web service. In this Petri net, the colors including parameters and user’s QoS (Quality of Service) requirements represent data flow. The time delay of transition is a function of colors in input place instead of time constant, which shows the dynamic property of Web service. The DTCPN allows the modeling of dynamic behavior of large and complex systems. Secondly, we give an algorithm for constructing composition of DTCPN model for an application composed of Web services. In order to reduce the complexity of model and the state explosion problem in reachability analysis of Petri nets, we give a reduction algorithm of DTCPN for four basic structures of the Web service composition. Finally, we discuss the correctness and time and cost performance of the Web service composition by reducing DTCPN model and analyzing the reachable service graph.