Research on Stateful Web Service Modeling Based on Extended Petri Net

In the environment of Internet of things, devices are encapsulated as web services and device operations are encapsulated as web service methods. These web services are stateful because devices can´t be controlled by more than one client at the same time. Traditional web service composition methods are lack of considering state of the web services and have great challenge under Internet of things. In this paper, a three-layer model for modeling stateful web services composition based on extended Petri net is proposed. It includes web services layer, ws-resource layer and process layer. A method of a web service is abstracted as a ws-resource. There are two types of ws-resources: exclusive resources can be invoked serially, non-exclusive resources can be invoked simultaneously. In this model, a web service is associated with one or more ws-resources, a web service can be invoked only when all needed ws-resources are available. Finally an example is demonstrated to illustrate how this model works.