Abstract
Since relational DBMSs are wide-spread, providing a relational global view for users who are only familiar with the relational model to access data in a multidatabase system is significant. However, the prior work on schema integration can not efficiently capture the relationships among relations from different databases. In this paper, we propose an approach to integrate database schemas into a relational global view which consists of concept hierarchies. A concept hierarchy is composed of relation schemes with the same concept, in which specialization and generalization can be specified to enrich the semantics of the relational view. Based on the concept hierarchies, a procedure is designed to decompose a global query to local subqueries and a set of transformation rules is developed to transform a query into an equivalent one for query optimization.