| Summary: | 碩士 === 國立東華大學 === 資訊工程學系 === 94 === The emergence of Web services has brought new insights into E-commerce applications. Web service composition is the creation of a more powerful Web service by the combination of elementary Web services. The concept of QoS (Quality of Services) is often used in service composition for selecting appropriate services from many alternative Web services. Appropriate services can be selected according to user’s preferences on QoS parameters. However, traditional approaches have largely ignored the fact that service dependencies can affect QoS in real-world and the execution characteristics of a workflow can also affect the effectiveness of service selection in workflow-based Web service composition. In this thesis, a service dependency-driven algorithm is proposed for selecting Web services in service composition. Dependency conflicts are solved by using the algorithm of maximal independent set in graph theory. Four strategies, namely, maximal dependency, maximal coverage, maximal discount and maximal improvement, are proposed for selecting dependencies. In addition, the exclusive execution characteristic of workflow components is analyzed and weighted to facilitate QoS computation. Incremental optimization is utilized to improve QoS in the case of parallel execution.
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