中文摘要：

针对 QoS 约束下的语义 web 服务组合的多个组合方案，提出组合质量概念，并改进组合算法以便快速获得高质量组合方案。针对组合质量的不同指标，引入质量平衡系数，构造可调节的启发函数，并增加到两步组合算法的后向搜索中，从而使用户通过调节质量平衡系数，获得预期质量的组合方案。为了提高组合速度，在高效数据存储结构的基础上，采用逐步变窄的前向搜索策略。基于前述改进的算法实现一个组合规划器。实验表明该规划器能够快速给出满足QoS约束的组合方案，且通过质量平衡系数的设置，能够给出满足预期质量的组合方案。

英文摘要：

Regarding many solutions in semantic web service composition under a given QoS constraint,a composi-tion quality concept was proposed,and an improved composition algorithm was designed to quickly generate a solu-tion with high composition quality. Concerning different criteria of composition quality,quality equilibrium coeffi-cient was introduced. And it was used to construct an adjustable heuristic function,which was applied to backward search of traditional two-step search algorithms. Thus,users can obtain a solution with desirable composition quality by adjusting the equilibrium coefficient. To improve efficiency,the composition algorithm adopted the gradual nar-rowing forward search strategy,which was based on an efficient data storage structure. On the basis of this improved algorithm,a composition planner was achieved. A series of experiments indicate that the planner can generate solu-tions satisfying given QoS constraint values. Meanwhile,by setting different values to the quality equilibrium coeffi-cient,the planner can produce a desirable composition quality solution.