随机QoS感知的Web服务组合概率分析

Probabilistic analysis for stochastic QoS of Web service composition

运行环境的开放性和动态性使Web服务的QoS具有内在的随机性。由QoS具有随机性的Web服务构造而成的组合服务,其QoS也具有随机性,从而使组合服务用户面临QoS需求不能被满足的风险。利用基于重要性采样的仿真方法,在随机PERT网络中对Web服务组合的QoS进行概率分析,以评估组合服务的QoS风险。方法通过一个简单的分布函数,引入权重函数以实现对目标分布函数的无偏估计。以实际的Web服务QoS数据为基础进行实验,对重要性采样技术和蒙特卡洛仿真的合理性和效率进行了对比,结果显示利用重要性采样技术进行组合服务QoS概率分析具有更高的精度与效率。

Open and dynamic network environments lead to the stochastic nature of Web service QoS(Quality of Service).Therefore,the Web service compositions which composed of these services will be inevitably random of the QoS.And theQoS requirements of Web service composition may not be certainly satisfied.In this paper,it analyzes the probabilisticdistribution of the stochastic QoS of Web service composition based on a simulation approach named importance samplingin stochastic PERT network.And it calculates the unbiased estimation of the target distribution function through aweighted function to a simple distribution function.Experiment has been done to show that the importance samplingapproach is much more rational and efficient than Monte Carlo simulation based on the actual QoS data of Web services.