一种对象代理数据库的跨类查询优化方法

对象代理数据库中跨类查询可以充分发挥对象代理模型的灵活性,为用户提供个性化数据服务,其执行效率十分重要。然而在处理多个跨类属性查询时,现有基于路径表达式的跨类查询实现存在对公共路径节点对象进行重复获取的情形,执行效率较低。针对跨类查询中加快获取终点对象的问题,优化核心思想是减少对路径上节点对象的重复与不必要的遍历,包括两个关键策略:首先是将路径节点整体作为虚拟路径视图统一获取节点对象,避免了多跨类属性查询下公共路径节点的冗余遍历;其次是针对路径复杂过长的跨类查询,依据代价估计策略选择物化查询涉及起点与终点对象,利用缓存减少执行时路径上中间节点的遍历。分别在属性数目与结果集规模两方面进行了对比实验,实验结果表明了优化方法的有效性。

A cross-class query optimization method of object deputy database

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.