An Ontology-Based Flexible Query Method for Semistructured Data

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.