In the traditional enterprise computing model, an Information Systems department use to maintain control of a centralized corporate database system. Mainframe computers, usually located at corporate headquarters, provided the required performance levels. Remote sites used to access the corporate database through wide-area networks (WANs) using applications provided by the Information Systems department.
Changes in the corporate environment toward decentralized operations have prompted organizations to move toward distributed database systems that complement the new decentralized organization.
Today’s global enterprise may have many local-area networks (LANs) joined with a WAN, as well as additional data servers and applications on the LANs. Client applications at the sites need to access data locally through the LAN or remotely through the WAN. For example, a client in Tokyo might locally access a table stored on the Tokyo data server or remotely access a table stored on the New York data server.
In a distributed database environment, mainframe computers may be needed at corporate or regional headquarters to maintain sensitive corporate data, while clients at remote sites use minicomputers and server-class workstations for local processing.
Both centralized and distributed database systems must deal with the problems associated with remote access:
Network response slows when WAN traffic is heavy. For example, a mission-critical transaction-processing application may be adversely affected when a decision-support application requests a large number of rows.
A centralized data server can become a bottleneck as a large user community contends for data server access.
Data is unavailable when a failure occurs on the network.
