半结构化数据查询的处理和优化

半结构化数据的特点是数据的结构不规则或不完整,其模型都基于带根有向图,因此,查询处理过程本质上是对图的搜索过程.另外,通配路径使查询处理更加复杂化.文章详细介绍了异构数据源集成系统Versatile中采取的半结构数据OIM(model for object integration)对象的查询和优化策略,包括查询计划的生成、路径扩展和路径索引、层次索引和基于数据源知识这3种查询优化方法.文章介绍的方法同样适用于其他的半结构化数据模型.

Querying and Optimizing Semistructured Data

Semistructured data has irregular or incomplete structure. In recent research on semistructured data sources and integration for heterogeneous data sources, models for semistructured data are based on direct graph with root vertex, so querying semistructured data is equivalent with searching in graph. In addition, path with wildcard characters brings more complexity in query processing. In this paper, the authors present the strategies deployed in querying and optimizing OIM (model for object integrating) data in Versatile-a system for integrating heterogeneous data sources. Algorithms for generating query plan and extending path are dis-cussed in detail and three optimization methods, path index (Pindex), level index(Lvindex) and knowledge of data source are introduced. Also the approach can be applicable to other graph-based semistructured data easily.