Research On Some Key Technologies Of Web Services Composition

As a new application model for decentralized computing, Web services composition is becoming an effective mechanism for the services integration on the Web. Along with the acceptance of Web Services as the mainstream technology for service provision, dynamic service composition based on Web Services has been regarded as one of the core technologies for the service-oriented computing paradigm. Many research institutions home and abroad have conducted quite a few researches on dynamic service composition, and have made some valuable achievements.However, Web service composition still has many problems need further study. We start our research according to the life-cycle of a Web service composition, and focus on the following key technologies in this paper: Formal model for Web services and Web services composition, Automatic Web services composition reason algorithm, Correctness verification of Web services composition, Exception handling approach for Web services composition. The major work and contributions of this dissertation are as follows:1. Putting forward a formal approach to model OWL-S based semantic web services atomic and composite processes operational semantic with Label Color Petri Nets (LCPN). It provides a more effective logical foundation to build dynamic web services composition model. Then, A Hierarchical Color Petri Nets (HCPN) Model named as "WSC_HCPN" for Web service composition is proposed. The model supports hierarchical describe of web service composition and presents the logical dependency of services graphically though Top-clown service decomposition method. Therefore the model can describe web service composition clearly and intuitively.2. According to the Web Services dependency rules, a reasoning Petri nets (RPN) model to represent the production rules of the available services in a local repository. Based on the RPN model, a formal reasoning algorithm was proposed to perform web services composition reasoning automatically. With the method of matrix operation used in the algorithm, the reasoning process of web services composition is accomplished more simply, quickly, and its efficiency is also improved due to the parallel operation ability of Petri net. Specially, it fits reasoning for the large-scale web services composition problem.3. Putting forward a Petri-Net-based formal verification technique to analyze and verify the services composition process in order to ensure the correctness and reliability of the composition. The approach consists of two parts involve structure verification and reliability verification. At first, It utilize Transitive Matrix analysis methods to analyze reachability of the composition model and check whether there are deadlocks. This method validates the structure correctness of composition model. Then, Describing the reliability attributes of basic web service, and the reliability parameters are introduced into Fuzzy Reasoning Petri Nets model of web service composition (FRPN) for simulating and verificating the whole reliability of Composite Web Services. The effectiveness of this method is proved by the results of the samples.4. Based on describing transaction type, transaction state and transaction dependency of web services by means of an intuitional formal presentation formal presentation. First, A ECA rule-driven expectable exception handling method for Web service composition was proposed and corresponding Petri net model was established. The advantage of this model is extensibility and adaptability. Then we propose a hierarchical exception recovery algorithm for unexpectable exception to ensure semantic atomicity of services composition. The algorithm determines the end compensation point dynamically in a hierarchical bottom-up manner according to transaction dependencies across hierarchies and diverse recovery behaviors of different services. The primary goal of it is to reduce the compensation sphere.5. A prototype named CPN4WSC is developed based on CPN Tools for web services composition. The usability and validity of the above methods and algorithms are proven by CPN4WSC.To sum up, this dissertation tries to do useful works on some key issues of dynamic service composition, with formal technologies of Petri nets and sets up concrete methods to solve these problems. We believe that our contributions make a nice groundwork for research and engineering on dynamic service composition both in theory and practice.