| With the rapid development of computer technology and Web services technology, users' demands for Internet are increased and users hope that Internet can provide needed services. As an open style for business, Web services have the characteristics of cover platforms, cover standards and cover languages, et al., which have gain the wide recognition of industry and academia. But, the function of single Web service is limited, therefore, users expect to realize customization and create business that can meet the demand of users by Web service composition. In addition, with the growth of SOA, composing independent Web services will be a new development trend; Web service composition technology is becoming the main one in enterprise information integration. Therefore, it is becoming the hot issue of how to utilize Web services technology to provide composition service that satisfies the function demand and performance demand.Web service composition involves many hot issues that exist in establishing time and running time respectively. The issues in establishing time include Web service matching, Web service selection, Web service automated composition and Web service composition verification, and these issues have important status during the lifecycle of Web service composition, the issues of running time include the implementation and monitoring, security and transaction. The dissertation mainly focuses on the four issues of establishing time and does some research, the main research work is as follows:1. To improve the correctness of Web service composition, functional attributes and non-functional attribute are considered, a hybrid service selection approach is given which is based on semantic matching and QoS attributes. When we need to select Web services for composition, two contents are focused: one is matching service schema which can realize the semantic matching between service interfaces parameters, in this dissertation, a semantic-matching based Web service selection strategy is proposed which utilizes matching technology to enhance the matching performance between Web service interfaces, the interface matching algorithm is proposed to realize the semantic connectivity; the other is selecting service instances, when several instances are running for one same service schema, one instance is selected by QoS attributes.2. Based on the composition optimization theory, we propose a QoS-aware service composition approach for a whole composition process, we mostly discuss the semantic matching and QoS constraints for Web service composition process based on genetic algorithm theory, corresponding genetic algorithm is given to expand genetic algorithm in application field, the algorithm for computing the whole composition process is proposed also, and based on the computing result, we can solve the problem of multi-QoS constraints and semantics constraints satisfaction. The approach can improve the performance of Web service composition process and decrease the computation complexity.3. To improve the flexility of process-based Web service composition and aim the abstract service node, we propose the approach about the local automated services composition, a model of Semantic Links Matrix(SLM) is proposed. Firstly, we build a SLM based on services library; secondly, based on SLM, we propose a back searching algorithm to realize the automated composition of abstract service composition. The approach is fit for the situation that the abstract service node has no corresponding concrete service and we only get the same function of abstract service intterface through service composition. The results of algorithm analysis and experiment show that the approach can improve the success rate and composition efficiency of Web service composition.4. In order to find problems about security, limitary and deadlock of Web service composition process, based on Petri net, we propose an approach to verify the correctness and validity of service composition model. We give the definition of services net and the algebra description of Web service composition, adopt Petri net to model several basal control flows and service compositions with basal or complex control structures, give the algorithm of creating Petri net model for Web services composition.
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