Using Ontologies for Database Query Reformulation

Query reformulation techniques based on semantic knowledge have been used in two ways in database management systems, namely for query optimization and for data integration. For the former approach, the main goal of query reformulation is to rewrite a user query into another one that uses less time and/or less resources during the execution. The main goal of the latter approach is to translate a user query into a set of queries which fit best the structure of the distributed sources. When using those query optimization strategies the transformed queries are equivalent to the submitted ones, i.e. they provide the same answer set, whereas when using data integration strategies a loss of information is expected. This paper presents a new approach of query reformulation using ontology semantics for query processing within a single relational database system. Here, the aim of the query reformulation is to extend the result of a given query in a semantically meaningful way. In fact, our approach shows how an ontology can effectively be exploited to rewrite a user query into another one such that the new query provides additional meaningful results that satisfy the intention of the user. Based on practical examples and their usefulness we develop a set of reformulation rules. In addition, we prove that the results of the reformulations are semantically correct by using a logical model.