The demand to accommodate old software to the needs of modern systems and the maintenance of ill-structured and ill-documented code triggered intensive research in software reengineering. But software (programs) are only a part of information systems. In this paper we will analyze the differences between reuse and reengineering of software and databases. In particular, we will address the problem of data migration, the problems of database fusion and the (unforeseen) demand to build application systems on top of independently developed existing databases. In some detail we cover techniques for the reengineering of database schemas in form of Entity-Relationship Diagrams and the concepts of federated databases which are envisioned by modern communication architectures, client/server solutions and the demands of enterprises to integrate information resources and to close gaps and bottlenecks in the information flow. We will introduce a technique for integration of independently developed schemas.

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