Web Service Composition Based On Dependency Graph Model

Web service composition is an effective approach to compose multiple simple Web services to complete a complicate task. When it comes to the large scale Web ser-vices, it is a challenge work to compose a Web service composition which satisfies both functional properties and non-functional properties quakily and effectively. In recent years, Web service composition has become a central research issue, many methods based on the graph model have been proposed to solve the Web service composition problem. In the thesis, we focus on the study of Web service composition problem based on dependency graph model, and further proposed solutions from three aspects.Firstly, we give a simple introduction on Web service composition problem. Then we proposed an Web service composition method based on the reduction of searching space. The method mainly consists of three aspects:(1) construction of Web service dependency graph,(2)the production of child nodes,(3)traversing the searching tree. We have detailedly introduced the construction of Web service dependency graph, in-cluding the initialization of Web service dependency graph and the process of adding dummy services. And we also proposed an algorithm to product the child nodes of the searching node, through this way, we can obtain less child nodes to reduce the search-ing space. Experimental results validate the method and show a good performance.Secondly, we propose a novel web service composition algorithm by integrating both QoS optimization and redundancy removal. The algorithm mainly consists of two steps:(1)the computation of QoS,(2)the removal of redundant Web service. We traverse the Web service dependency graph forward and compute the QoS, then traverse the Web service dependency graph backward to select the Web services which have the best QoS and remove the redundant services. Experimental results have proven that our algorithm keeps less redundant services remained in the solution while keeping very good QoS performance.Finally, considering about the adaption of Web service composition in the dynam-ic network, we propose a repairing method for the broken Web service composition. The method mainly consists of three phases:(1)removing the broken Web service and its succeeds,(2)Discussing wether it can be repaired or not,(3)re-computing the QoS and obtain the next optimal Web service composition. Experimental results show that the repairing method is more efficient than the re-composition method.