This book presents the techniques for the design and use of multidatabase systems — those which generalize database systems with features for shared access to multiple databases, while preserving the local autonomy, the heterogenicity of existing data, and the existing applications. It describes the concept, the need, and the evolution of the database systems; addresses issues of reference architectures, semantic heterogenicity, and autonomy; discusses the user interfaces, and proposals for multidatabase languages for popular types of databases: SQL, OO, information retrieval and knowledge bases; considers the internals of multidatabase systems, e.g., system architectures, gateways, query, and transaction processing; discusses prototypes and commercial multidatabase systems; and presents the emerging standard, e.g., RDA, SQL-Access.