关键词: 对象代理数据库, 跨类查询, 路径表达式, 虚拟路径视图, 物化路径选择策略

Abstract:

Cross-class query in object deputy database can make full use of object deputy model’s flexibility to provide users with personalized data services, and its efficiency is very important. However, using existing path-expression based methods to handle cross-class query with multiple attributes, the query performance degrades due to redundancy of common path nodes. To solve the problem of terminal object's quick acquisition in cross-class query, we propose an optimization approach to reduce the repeated and unnecessary traverse of common node objects in the path. Our approach consists of two key strategies. The first strategy is to consider the whole path nodes as a virtual path view, so we can obtain node objects uniformly and avoid redundant traverse of common path nodes in multiple cross-class attributes query. The second strategy aims to materialize common path nodes to handle cross-class query with a too long path. We select the origin object and the terminal object of materialized query according to the cost estimation strategy. Particularly we leverage cache to reduce the traverse of intermediate nodes. Comparative experiments on real data regarding both the number of attributes and the scale of result sets verify the effectiveness of our optimization method.

Key words: object deputy database, cross-class query, path expression, virtual path view, selection strategy of path materialization