Abstract: This paper analyzes the integration system based on mediator/wrapper and its feature of query in detail. According to the fact that global join query involving more than several datasources is the main query type and its cost of query is very high, we considers global join query as the main object to be optimized. At the same time this article puts forward optimization of join query based on semijoin. This paper presents the directed weighted graph of semijoin in order to optimize semijoin execution plan. Furthermore, the fast and effective optimization algorithm is presented in order to produce optimum semijoin execution plan based on directed weighted graph of semijoin.

Key words: Mediator/Wrapper, Query optimization, Semijoin, Directed weighted graph of semijoin, Algorithm for minimal branch flow to fixed end-point

摘要： 在对Mediator/Wrapper集成系统及其查询特点进行详细分析的基础上，针对涉及多个数据源的连接查询是使用频率较高且是查询代价最高的一种查询方式这一事实，确定了以全局连接查询为主要优化对象，并提出了用半连接方法来优化连接查询。在对半连接执行方案进行优化时，提出了半连接加权有向图的概念，并给出了针对半连接加权有向图的半连接执行方案的快速有效的优化算法。

关键词: Mediator/Wrapper, 查询优化, 半连接, 半连接加权有向图, 固定终点最小分支流量算法