【摘要】 <正> 1.引言传统的查询优化器利用语法变换对查询进行优化,从生成的查询计划中选择一个具有最小代价的执行计划。然而,随着数据库技术和网络技术的发展,尤其是在异构数据库环境下和面向对象的数据库中,处理的对象结构更为复杂,传统的查询优化器显得力不从心。语义查询优化利用数据库上的语义规则将一个查询变为一个语义等价且更加高效地查询,以此来弥补传统查询优化技术的不足。虽然,语义查询优化能够产生较好的优化效果,但必须有效地解决以下一些问题:更多还原

【Abstract】 Semantic query optimization (SQO) is comparatively a recent approach for the transformation of given query into equivalent alternative queries using matching rules in order to select an optimal query based on the costs of executing alternative queries. With the development of database technology and new applications of information systems,data become more complex and heterogeneous. In such situation,traditional query optimization technology is not very suitable. Therefore,since the early 1980’s researchers regarded SQO as a promising technique. But no extensive implementations of SQO exist today due to some key problems have not been solved efficiently. In this paper,we survey the research in the area of SQO,point out the process of current research and future directions.更多还原