中文摘要：

一个组合服务可以由多个具有不同QoS属性的服务合成,由此带来的一个问题是如何将QoS属性作为条件选择最合适的服务以满足组合服务的全局QoS需求.针对这个问题,提出了利用分层图技术对复杂的服务组合过程模型进行化简,将服务选择问题简化为有向图中的选路问题,这样在服务选择时就无需考虑不同的流程结构（例如,顺序、选择、并发和循环结构等）,从而降低了服务选择算法的复杂性,提高了执行效率.在简化模型的基础上,给出了一个基于自适应遗传算法的QoS感知的组合服务选择算法.仿真实验表明该方法是可行和有效的.

英文摘要：

A composite web service can be constructed by combining together the component services which have different non-functional QoS （quality of service） attributes.A problem is thus caused,i.e.,how to select the most suitable services in accordance to the different QoS attributes as criteria as to meet the global QoS requirements of the composite web services.To solve the problem,an approach is proposed to simply the complex process model of the composite service with the layered graph technique used to reduce the problem to be a routing problem in directed graph.Then,the selection algorithm for the composite service is performed taking no account of different flow operations,such as sequence,selection,concurrency and loop,thus reducing the complexity of selection algorithm and improving execution efficiency.According to the simplified model and based on adaptive genetic algorithm,a QoS-aware selection algorithm is given for composite web services.Simulation results showed that the proposed approach is feasible and effective.