Researeh On Web Service Discovery And Service Composition With QoS Constrained Driven

With the rapid development of Web services technology, computer software applications gradually shift from static closed model to dynamic opening model. Software develop to meet new applications by reusing and combining and it can be developed to improve development efficiency and save resources.In the complex environment of the Internet, how to provide effective and needed Web services become a research hotspot in the current service calculation domain.This paper mainly studies Web service discovery, composition and selection strategies which based on QoS-constrained.Firstly, some Web service discovery models have many shortcomings at present , for instance functions is imperfect, lack of feedback mechanisms, lack of scalability,can not meet the needs of preferene users and other shortcomings,and in view of this, this paper propose a QoS-constrained Web service framework which suposes Web service discovery and composition (it named WebDAC). First of all,WSDL and UDDI was modified to support non-functional descriptions and Web scalability in the framework model; Then, in order to ensure the assessment of quality be authenticity and validity, we introduce a Web service evaluation system which support Web service monitoring and feedback ; The model also improve function of service selection which enter to the local selection stage or global optimization selection stage, according to the type of service which user'needs (a single Web service or a combination of Web services), meanwhile individual customers can set different weight based on their own needs to satisfy preferene needs.Secondly, this paper analyzes the advantages and disadvantages of the current model of service quality, and based on this, it have established two models of service quality which is objective and comprehensive. The two models are named single-service QoS model and the composite service QoS model. In the single QoS model of service ,we define and quantify the seven property parameters including execution time, delay time, reliability, cost, safety and reputation meamwhile introduce the concept weights and service requests weight, finally,it has formed a comprehesive QoS evaluation model.;QoS model of composite service is based on the single QoS model of service and consider the four structured process of sequence, selection, parallel and cycle which establish a comprehesive QoS evaluation model of composite service.Finaly,in the service selection, we consider two selection strategies which are local selection and global optimization strategy. Local selection strategy satisfies uers'functional requirements of Web service and estimates Web service's non-functional criterions dynamically based on the criterions registered by Web service,information fed back by users and service's realtime data, in order to evaluate Quality of Service dynamically and real-time updates, ensures that QoS information is impartiality,trustworthiness,and real-time by the four-stage selection algorithm;In the past, the people using linear programming and genetic algorithm to study the optimization of composite service.In this paper Tabu search algorithm will be applied to Web services composition optimizatio.We propose a new selection strategy of composite service which is based on Tabu search algorithm;Tabu search algorithm is an extension of local neighborhood search, and it is a global optimization algorithm step by step.The experimental results show that the algorithm is practical and effective.