A Petri-net and QoS Based Model for Automatic Web Service Composition

Web services are widely used because of their features of interoperability, loose-coupled and platform independent. Web services composition is one of the most popular topics in service computing area. In this paper a method based on Petri net coverability problem and utility of Web services is proposed to handle automatic service composition. The former is for satisfying functional requirements of service composition while the latter corresponds to non-functional properties. For a set of given services, each service is translated into component of Petri net and the input/output places with same semantics are merged. According to user’s input and desired output, the initial marking and target marking can be obtained. Then the coverability tree and coverability graph can be constructed. Next, the nodes on the coverability graph which can cover the target marking should be find out. If there are more than one coverability paths, we determine the smallest weight denoted as “SW” on each path. The weight is defined as the utility calculated according to the QoS. At last, services on the path with largest SW are selected as service executing sequence to reach the goal of automatic service composition.