Abstract: In service oriented application，value-added service is composed of some component services which are selected from candidate services.By analysing the characteristics of the composite services，both QoS and semantic relations between component services are regarded as criteria for selecting a set of services to construct a composite service.This paper presents a semantic relation model for the service composition，in which the data logical relationship and the condition dependence are comprehensively considered.Based on the model，service selection is formulated as a multi-objective optimization problem.Genetic Algorithm（GA） is used to search for a solution.Experimental results show that the proposed approach is feasible and effective.

Key words: Web services composition, service selection, Quality of Service（QoS）, semantic relation, data logical relationship, condition dependence

摘要： 在基于服务的应用中，增值的Web服务可以通过在候选服务中选取一些服务（即服务组件）组合组成。通过分析组合服务的特性，将QoS和服务组件间的语义关联度作为组合服务选取的重要指标，提出了组合服务的语义关联模型，模型综合考虑了服务间的数据逻辑关系以及条件依赖关系对于组合服务的影响，基于该模型将服务选取问题形式化为多目标优化问题，采用遗传算法（Genetic Algorithm（GA））求解。实验结果表明该方法是可行而有效的。

关键词: Web服务组合, 服务选取, 服务质量, 语义关联, 数据逻辑关系, 条件依赖关系