16 - Distributed database systems

Abstract

A distributed database (DDB) is managed by a distributed database management system (DDBMS) that keeps track of how the data is distributed as well as provides the usual DBMS functions. This chapter discusses the extended library scenario. A first-level E-R model for the extended library scenario is illustrated and distributed database design is explored in the chapter. Data may be distributed by fragmentation and replication of tables. Distributed data independence is discussed in the chapter. Fragmentation, replication, and location transparency are aspects of distributed data independence, the advantage of which is that the way the data is distributed can be changed as necessary without affecting existing programs. A distributed database is potentially very complex to design and manage compared with a centralized database. The situation is much easier to manage if there are restrictions on updating the database.