Distributed database system (DDBS) technology is the union of what appear to be two diametrically opposed approaches to data processing: database system and computer network technologies. Database systems have taken us from a paradigm of data processing in which each application defined and maintained its own data (Figure 1.1) to one in which the data is defined and administered centrally (Figure 1.2). This new orientation results in data independence, whereby the application programs are immune to changes in the logical or physical organization of the data, and vice versa.