Research On Performance Evaluation System Of Web Service Composition Based On Petri Net

The nature of Web services composition is to flexibly achieve upper business needs through communication and collaboration between Web services, and can mask the impacts which are the underlying implementation technology changes haven on the upper. Web services composition is the primary means to build new services and meet business needs in Service-Oriented Architecture (SOA), and is at the core position in business processes’ construction and reorganization. Therefore, the performance and performance evaluation methods of Web services composition are important to the development of SOA.Supported by the National High-Tech Reaearch and Development Plan (863) of "the researches about key technologies and performance evaluation of dynamic Web services composition", we discuss on the performance evaluation of Web services composition from two views which are qualitative analysis and quantitative analysis, and we research on the related key technologies. The main contributions are as follows:(1) In order to monitor the quality of Web services composition in all aspects of the period from Web services composition’s generation to its end, this paper proposes a kind of performance evaluation architecture for Web services composition which is throughout the entire lifetime of Web services composition. The architecture consists of two closed-loop negative feedback systems. The one provides qualitative analysis for the performance of Web services composition, and the other one offers quantitative analysis for the performance of Web services composition. In order to achieve the performance evaluation architecture, this paper proposes a performance analysis model WSCPAM for Web services composition, which is based Stochastic Petri Net. And the two inherent structure constraint conditions of WSCPAM are discovered. WSCPAM is the material basis of the architecture, on which all performance evaluation jobs by the architecture are carried.(2) To be able to discover the inherent Fatal weaknesses of the structure in the design phase and ensure run-time Web service composition is good structure, this paper gives the meanings of conducting various structural verifications (including structural constraint conditions verification, liveness verification, boundedness verification, deadlock verification and trap verification), and provides algorithms to implement these verifications. (3) In order to effectively using WSCPAM model to conduct performance quantitative analysis for Web service composition, this paper presents a detailed and complete algorithm for converting WSCPAM model to isomorphic Markov chain. The algorithm mainly includes three rules, which respectively are conversion rule, evolution rules and merger rules. The Partial correctness of the algorithm is proved by Floyd invariant assertion method. The Termination of the algorithm is proved by well-ordered set method. The algorithm is completely correct, which can be illustrated by the conclusion which is that the algorithm is partial correct and can be terminated. The time complexity analysis of the algorithm shows that the algorithm is effective. Using the generated Markov chain, a number of performance indicators of WSCPAM model can be calculated.(4) The performance of Web services composition plays an important role in improving the virtuous integration of the value chain at the core of services. For how to effectively identify the performance bottlenecks of Web services composition, this paper proposes two performance bottlenecks location strategies BNL-WSCPAM and BRF-WSCPAM.Based on the all direct relationships between place node and transition node, four basic structures of the model are summarized. And the completeness property of the four basic structures is proved, which means the different compositions between the four kinds of direct relations can represent various Web services combinations. Through structural conversion, an analysis structures set is obtained, which includes Sequence structure, Split structure and Join structure, and is used to predict performance bottlenecks that may exist. On the basis of the set, the paper presents the performance bottlenecks location strategy BNL-WSCPAM for Web services composition. According to time-related performance indicators, the strategy classifies different types of places. Under the various distributions of different types of places in three kinds of analysis structures, the performance bottlenecks that may exist have been discussed through the Down Arc Analysis method and Reverse Arc Analysis method. This paper also gives Structure Discovery Theorem, which is used to determine the three kinds of analysis structures. The experimental results show that the prediction of the strategy is valid.It is different from BNL-WSCPAM that the performance bottlenecks location strategy BRF-WSCPAM is solely based on performance indicators. Through analyzing the obtained performance indicators in previous works, it finds these performance indicators which make large contribution for bottleneck generation. And then through normalize these indicators, a comprehensive performance parameter-Bottleneck Risk Factor is obtained. Based on the parameter, all transitions in WSCPAM are uniformly measured, and some bottlenecks may be found.