Research On Real-time Petri Net Strategy For Exception Handling Of Web Services Composition’s Dynamic Execution

With the development of the internet technology, applications are developed by different program languages and running in different platform, which will make trouble for the interaction among them. The service oriented computing technology is put forward to solve this problem. Web service as a very important technology is widely used in oriented service computing, and it can shield the implementation details of application. Web service uses XML to release its interface so that different applications can easily interact by using web service.But with the constantly growing of the internet,a large number of Web services have emerged, and complex needs can not often be realized by a single web service. We need to combine different web services according to the needs of users.Meanwhile, Web services are deployed in a complex network environment and will be easily effected by network congestion, infrastructure damage, abnormal attack and so on. Exceptions of web services will be triggered because of the reasons above. If we do not handle those exceptions properly,the execution of web service composition will be terminated.As to the above problems, this paper designs a Petri net based execution engine. Firstly, the relationship between services and Petri net is established and the Petri net of web service composition is initialized. Then the engine detects the transitions that can be executed by using the firing rule of transitions in Petri net. The transitions in the selection relationship may be selected through the algorithm for eliminating conflict that is proposed. Finally, the engine executes all services corresponding to the transitions simultaneously and then feeds back the dynamic execution information of services to the Petri net. Repeating the above process until the execution of composite services is done. Besides, we put forward the method of validating the type and grammar of demand parameters, the method of converting parameters among services and the method of checking output parameters an so on.Then, Petri net real_time strategy for exception handling of web service composition is proposed in this paper. We can effectively reconstruct service process by using Petri net when exception occurred. The service composition net that is reconstructed can be verified through Petri net theory, which ensures the correctness and data consistency of service process, and replacement strategy fully considers the transaction property. The compensation mechanism is used to guarantee the data consistency. The semantic function tree is proposed for indexing services, which will help the execution engine to find the replication solutions as more as possible.Finally, the execution engine is verified through a real example. The exception handling algorithm is verified through experimental scenarios. Then the execution engine and the mainstream execution engine were compared, which helped us find the advantages and disadvantages of the research and points out the direction of future work.