| With the increasement of web services, many web services will offer the same services, and the clients will demand more values added and informative services rather than those offered by single and isolated web services. As the result, the problem of synthesizing web services with high quality will be raised as a prominent issue.The clients will face the trouble of choosing or creating composition plans, among numerous possible plans, that satisfy their Quality-of-Service (QoS) requirements.Typical QoS properties associated with a web service are execution cost and time, availability, successful execution rate, reputation, and usage frequency. In engineering perspective, generating the composition plan that fulfills a client's QoS requirements is a time-consuming optimization problem.Based on the existing service composition, web service composition supporting QoS constraints is studied in this paper. In order to carry out the semantic description to QoS of Web service, the OWL-S is extended, and QoS ontology model with the ability of semantic description is constructed by comparing the advantages and disadvantages of DAML-QoS ontology and WSMO-QoS ontology model. OWL-S-QoS ontology model has good expansibility and supports for a variety of measurement methods. It can meet the needs of service description better, and is in line with international norms and achieves forward compatibility. An OWL-S-QoS-based ontology Web service discovery model is constructed, and three levels matching algorithm of Web service is implemented according to Web service description model. This algorithm is a top-down process and refined by steps, not only meets various needs of users in some fields, but also decreases the influence of false published information for services' QoS evaluation to the lowest level. For the combinatorial optimization problems, a web service composition algorithm combined of tabu search and simulated annealing and a structure supported this algorithm are proposed. This algorithm assigns a high-quality Web service to the atomic process of combination mode in an optimization approach which not violate QoS constraints, featured mixed meta-heuristics, and combine tabu search with simulated annealing. It can not only find a combination planning to meet the constraints, but also reduce the computational burden of searching planning. The architecture supports to generate QoS-oriented Web service combination planning automatically in friendly way to users, and it is combined of a combination agent and implementation planning optimizer. The combination agent is for the candidate web services discovery and the execution plan optimizer implements the proposed composition algorithm.Good performance of this combination algorithm is demonstrated, comparing with the Integer Programming approach in simulated environment. |
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