| The Internet is now undergoing an evolution from a traditional platform for sharing information to an open distributed computing infrastructure. With more and more data resources,computing resources and applications wrapped and abstracted by "services" to be accessible via the Internet for public usage,service composition becomes the natural way for dynamic resource aggregation and flexible application intergration.Especially,along with the appearance and promotion of Web Services as the mainstream technology for service provision,in recent years dynamic service composition based on Web Services consequently has been regarded as a hot research topic in the area of distributed computing.To address the requirements of integration among different heterogeneous systems in enterprise application, then meet the dynamic client requirements of business, we have investigated some related issues of dynamic service comosition,focusing on using the Petri net to optimize, analyse and verify the service composition plan. For the situation where there have still been many problems in Web service composition researchs which involve Web service automatical composition, synthetic service process verification, synthetic service optimization, etc., we have done comprehensive work in this dissertation as follows:(1) In order to solve how to obtain the optimal service composition plan when there is more than one service composition plan which can meet the client requirements, an approach of selecting the optimal web services composition plan based on Petri nets was proposed.Compared with the current numerous related research in service compositon,this presented method has several innovations. According to web service library and the client requirements, Incidence matrix is obtained, then using the Basic Solutions of non-odd equations, all potential plans of service composition are gained. And the generalized stochastic Petri net (GSPN) is employed to analyze the performance of the plan, then the optimal web services composition plan is obtained.(2) In order to optimize the performance of web services composition, an optimization composition algorithm based on the behavioural relation of Petri net is proposed which is to meet the client requirements, according to the current web services, and to obtain the web services composition plan with the best performance automatically. This algorithm uses Petri net to model the data flow, adopts the reachable marking graph to analyze the performance, further, and extracts the behavioural relation among transitions and among transition sequences, to obtain the cheapest composition structure.(3) In order to solve the problem in selecting proper composition service that if we only take functional demand into account, we can meet the client requirement in behavioural constraints. Petri net is adopted as a formal tool for the specification of Web service process model. Meanwhile, the Petri net model which represents for the service request's process model is established for the constraints of client composition service request's behaviour. Then we can select the proper composition service which can meet behavioural constraints by behavioural congruence judging algorithm proposed, so as to improve the accuracy of classification. In order to simplify the judgement process, we program prototype system with Visual C++. Figure [19] table [4] reference [57]... |
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