Federation provisions data without additional persistence or duplication of source data. A federated database system maps multiple autonomous database systems into a single federated database. The constituent databases, sometimes geographically separated, are interconnected via a computer network. They remain autonomous yet participate in a federation to allow partial and controlled sharing of their data. Federation provides an alternative to merging disparate databases. There is no actual data integration in the constituent databases because of data federation; instead, data interoperability manages the view of the federated databases as one large object (see Chapter 8). In contrast, a non-federated database system is an integration of component DBMS’s that are not autonomous; they are controlled, managed and governed by a centralized DBMS.

Federated databases are best for heterogeneous and distributed integration projects such as enterprise information integration, data virtualization, schema matching, and Master Data Management.

Federated architectures differ based on levels of integration with the component database systems and the extent of services offered by the federation. A FDBMS can be categorized as either loosely or tightly coupled.