The Research On The Scheduling And Execution Engine For Web Service Composition Based On Petri Net

With the development of SOC(Service-Oriented Computing), a single web service hasnot met the business requirements of service requesters because of the conflict betweenservice granularity and flexibility. So there is no denying that web services composition iscoming. Indeed, the true potential of web services lies in web services composition. Currently,there has been various kinds of researches in this field, including studies based on Petri nets.However, the automatic generation of Petri net cannot be easily obtained in these methodsduring the process of web services composition, and hardly realize online analysis andcoordination scheduling towards web services. The main reason for these problems is that it ishard to avoid the state explosion when carrying out state analysis towards Petri nets.Meanwhile, these researches also lack of a flexible and simple Petri net model, and overlookan unified and symbolized form which can vividly describe web services’ structuralrelationships. Therefore, all above these will lead to the fact that some studies only pay theirtopic attentions to web service modeling and offline analysis based on Petri net, and cannotrealize collaborative invocation, which will exert much influence on the efficiency ofservices’ execution.As to the above problems, in this paper some studies on web service based on Petri netwere carried out and have obtained some certain innovative achievements as follows:First and foremost, Petri net with semantic markups is used as web service model in thispaper, and each service is described with PNML(Petri net Markup Language)+OWL(Ontology Web Language). So the semantic relevance can be created between web servicesrecording to the domain ontology, and then web services are composited through sharingsynthesis of Petri nets.Further, although the Petri net of web services composition or the composite web servicecan present all kinds of structures between web services, it is not easy to get the specificrelationships. So in this paper the basic structural relationships will be analyzed in details,including sequence, concurrence and selection. And then synchronization and controlledconditions are also talked about. In addition, the concept of web service executable sequenceis defined. Accordingly, the web services’ executable planning algorithm using Petri net is put forward and its executing results will be conductive to web services’ co-scheduling and failurerecovery.Last but not least, as to all kinds of structural relationships between web services, aco-scheduling strategy is given respectively. Regarding the semantic relevance in PNML+OWL and web service executable sequence，a new method based on Petri net is proposed tohandle multiple web services’ coordinated invocation. Finally, the scheduling and executionengine for web service composition is designed and developed. So it can further verify thevalidity and effectiveness when Petri net theory is applied to the actual web services.