In a distributed database, data is stored across several sites managed by a DBMS capable of running independently. A distributed database (DDB) is a collection of multiple, logically interrelated databases distributed over a computer network. A distributed DBMS is then described as the software system that allows the management of the databases that are geographically located at different places and creates the distribution transparency to the users [3].

Figure 10.1 explains the basic concept of a centralized DBMS and a distributed DBMS. As illustrated in the figure, in the centralized DBMS, a central data storage resides in the center, and all the terminal uses a network to communicate with the central storage. In a distributed DBMS, the storage facility is distributed at multiple sites: