Integrity Constraints in Federated Database Design 1

In this paper we demonstrate the application of a methodology for federated database design. Federated database design includes the transformation of heterogeneous local schemata from the native data models of the component database systems into a common data model, the integration of these homogenized schemata into the federated schema, and the derivation of external schemata for global applications. Our methodology seamlessly captures all phases from schema transformation and integration up to derivation of external schemata. Our approach di ers from other recently proposed methodologies because we consider integrity constraints throughout all phases and use them for resolving con icts. Therefore, the main focus of this paper is the treatment of integrity constraints and their evolution in the federated database design process. For resolving con icts which arise during the transformation and integration process the consideration of integrity constraints can be useful, although the process becomes more complicated. Taking constraints into account provides a better understanding of con icts. The constraints can be used to judge possible resolutions of con icts. For certain kinds of con icts we have to add new global constraints, but often there is not a unique and predictable choice of additional global constraints. The way of resolving such con icts also depends on the intended semantics of the federated schema and, thereby, on the intended global applications. Sometimes, situations arise where there is even not a consistent solution for all con icts together. Therefore, a methodology for federated database design must be prepared to make compromises.