a. Homogeneous vs. heterogeneous distributed database system
Homogeneous database systems involve similar databases distributed over the network (on separate machines). Example of homogeneous database system is an enterprise’s nation-wide ERP system which comprises of distributed databases, all of which are Oracle. Heterogeneous database systems on the other hand are distributed database systems that consist of at least one different database. Example of heterogeneous database system is an enterprise wide intranet application which consists of databases such as MS SQL server and DB2, which belong to the same integrated database application.
b. Autonomous vs. Non-autonomous distributed database system
Autonomous and Non-autonomous distributed database is a sub-set of Homogeneous databases. Autonomous distributed database are independent databases (separate data residing in each database) that function independently, but, are integrated by the controlling application software. Non-autonomous distributed database are homogeneous databases where data is distributed across homogeneous nodes and is controlled by DBMS at each node. Example for a autonomous distributed database system is Oracle based data marts which manages data pertaining to sales, distribution and inventory. Example for a non-autonomous distributed database system is Oracle based global sales database which is partitioned across multiple databases.
c. Federated vs. Unfederated
Federated database systems are collection of heterogeneous database systems which is integrated together to function as a single system. Each constituent database system is autonomous and control can be exercised to each local database component of the federation. Unfederated database systems are collection of homogeneous database systems which are generally non-autonomous by nature and employs centralized control. Example for a federated database system would be an extended heterogeneous distributed database system that span across multiple database vendors and multiple enterprise departments. Example for unfederated database system would be an extended homogeneous distributed database system that spans across a global enterprise function.