Reening Extensional Relationships and Existence Requirements for Incremental Schema Integration 1

Schema integration as part of the database design as well as of the database integration process has to deal with extensional relationships among classes of the di erent schemata to be integrated. As a rule, the extensional relationships must be speci ed by the database designer. Partially, some relationships may also be derived from other relationships. Most existing schema integration approaches consider relationships only between two classes. A correct and complete schema integration, however, can only be performed if all extensional relationships among all classes to be integrated are completely and correctly speci ed. In this paper we present an incrementally way to support this. Usually, an ad hoc speci cation of extensional relationships by the database designer is often not feasible. Therefore, we develop a method to derive extensional relationships from an incomplete speci cation. From these relationships an integrated schema is derived which is only partially correct and can be used for further extensional relationship re nements and corrections. In this way we support an incremental process of schema integration.