基于视图自维护理论的高效视图维护机制

Efficient View Maintenance based on View Self-Maintenance Theory

1 介绍 多库系统中的全局视衅是在全局数据模式上定义的,而全局数据模式由各局部数据库(Local Database: LDB)的数据模式通过异构模式消解得到.因此,对全局视图的存取操作要分解为针对多个LDB的子操作,可能还要对数据模式及查询语言进行相应的转换.如果每一次对全局视图的访问都要转换为底层数据库的访问,代价是很昂贵的,所以多库系统一般都保持物理的全局视图.底层关系的修改会导致全局视图的改变,因此在保存物理视图的多库系统中,当底层关系发生变化时,要对全局视图进行视图维护,使其与底层关系保持一致.

A materialistic view in multidatabase is derived from base database that may not reside at the multidatabase. Maintaining these views efficiently in response to base update is difficult. This paper considers the problem of view self-maintenance, including how to maintain a view and how to determine whether a view is maintainable. Then we combine the theory of self-maintenance with application,and provide a new multidatabase self-maintenance algorithms :EMVM. Our new algorithms make full use of the information in multidatabase views,and minimize the number of queries sent to the local database systems for view maintenance ,which makes the multidatabase system more efficient.