【摘要】 半结构化数据库没有固定的库模式,用户对其结构难以产生清晰的认识,从而无法有效地查询所需的内容.提出了一种基于本体的柔性查询,用户通过了解数据库本体语义信息而发出的查询不必遵循严格的数据库模式也能得出结果.由于在半结构化数据库上直接查找效率很低,故在其上生成描述结构模式的概念本体库.查询模块先在本体库上评估能否得出查询结果,再在数据库上执行查询.然而由于本体库可能是图的形式,其查询代价仍然很高,本质上是NP问题,进一步研究了将图转化为树的方法,并给出了相应的算法.更多还原

【Abstract】 Due to the lack of stable schema in semistructured database, it is hard for users to obtain a clear view of the structure and employ efficient queries. An ontology-based flexible query method is presented in this paper. Based on the understanding of the ontology semantic of database, users can pose customized query without following the strict data schema. In contrast to the low efficiency in direct search on semistructured database, a concept ontology library is developed, which represents the schema of the original database. The query module first evaluates ontology library prior to the actual execution on database. However, the query cost is still high if the data schema of the ontology library is graph, which is essentially an NP problem. Thus in order to reduce the query cost, a method of transforming the graph to a tree under the flexible semantic and the corresponding algorithm are developed.更多还原