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The problem of Web services selection based on quality of service (QoS) hasn't be essentially solved by the single objective optimal algorithm which optimizes service selection by aggregating multiple QoS parameters to form a composite objective function using weighted scoring method. This paper presents a Web services selection algorithm of QoSaware and global multi-objective optimization, termed WS-SPEA2. The essence of the proposed algorithm is that the problem of Web services selection based on QoS is transformed into a multi-objective services composition optimization problem with QoS constraints. A strength Pareto evolutionary algorithm (SPEA2) is utilized to produce a set of Pareto-optimal solutions by means of simultaneously optimizing a series of objective functions, that is, minimizing service cost(C) and service time(T) with the constaint of satifying the parameters reputation(RE), reliability(R) and availability(A). And the users can select one from these solutions for their preferences. The results of a series of simulation experiments indicate the feasibility and efficiency of this algorithm.

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Currently the research on the Quality of Service (QoS) composition in ASKALON grid workflow management system is still rare,a computational method of activities' QoS of grid workflow is proposed based on abstract grid workflow language(AGWL) model.Existing grid workflow scheduling algorithms commonly suffer by one or several of the following drawbacks:monotonous expressing structure ,not enough consideration of multidimentional QoS parameters and single objective optimal scheduling .A scheduling algorithm of multiobjective optimal grid workflow scheduling with QoS constraints based on multiobjective particle swarm optimization(MOPSO) algorithm is proposed, compared with a grid workflow scheduling algorithm based on NSGA-Ⅱ algorithm,the experimental results show the validity of algorithm.