A federated database system (FDBS) is a set of autonomous and possibly heterogeneous databases that have to work together. This paper provides a thorough review of the issues surrounding federated databases. Architectural issues addressed include both loosely coupled and tightly coupled FDBSs as well as a five-level schema architecture. The authors discuss both bottom-up and top-down methodologies for developing an FDBS. They cover both development and operational issues for an FDBS in depth. The discussion of types of heterogeneity and autonomy is especially well done. Parts of the discussions on transforming processors and component schemas are hard to follow.

The paper focuses exclusively on the technical issues, but in the future, FDBSs will be an important subject from the user perspective. Organizations will have to provide access to autonomous, distributed, and heterogeneous databases on an enterprise-wide basis. Individuals will also want to use online systems that can access disparate database systems simultaneously. As a result, the paper serves a valuable purpose as a basis for future research work. The benefits from reading this paper will only be gained by people who have a strong background in database management technology. A shorter version of the paper, with a focus on clarifying the key issues for the computer professional who is knowledgeable about DBMSs but is not an expert, would be valuable.