Growth of cleint server systems
The introduction of large numbers of PCs and networks into the workplace led to the development and widespread adoption of client-server systems in the 1990s. This development has been significant to the growth of distributed databases. Distributed databases require processing power at each site where data is physically located. Processing power is also usually required at each individual workstation to resolve the complex issues of where and how data should be stored and retrieved in a distributed database environment. Client-server architectures provide processing power at all locations. In a traditional mainframe architecture, the combination of processing power and data storage is located at only one site – implementing a distributed database is not possible.
Although client-server systems are usually identified with distributed data storage, there is no requirement for data storage to be distributed in client-server environments – data may be centralized on one mainframe, distributed widely throughout the organization, or anything in between. Many organizations have seen the ability to move to client-server as an opportunity to replace their expensive mainframe data centers with less expensive minicomputers and microcomputers. Such a strategy has come to be known as downsizing or rightsizing. With the cost of good RDBMS software for mainframe systems at around $250,000, the lure of using smaller Unix-based systems running RDBMSs costing $10,000 is strong (Burleson, 1994, p.91).
The use of client-server has not proven universally successful, however. A 1994 survey by the Gartner Group (as cited in Applegate, McFarlan, McKenney, 1996, p. 372) estimated the move to client-server to cost an additional $50,000 to $65,000 per workstation over a five-year period. Many organizations also underestimate the work involved in training users to operate, and support staff to maintain these more complex systems and networks. One estimate places the cost and effort of maintaining the network and distributed information architecture in client-server architectures at 40 percent (Ryan as cited in Applegate, McFarlan, McKenney, 1996, p. 372). Many IT managers fail to recognize that moving to client-server may cause their support staff requirements to grow by double or more in size, especially when many geographically dispersed sites are involved or the user population is not familiar with the use of client workstations. The added costs of such systems have soured some firms on the technology and slowed its implementation. These recent lessons highlight the importance of implementing client-server as a strategic transformation of the organization’s IT architecture, rather than simply a replacement for older technologies.
In the last few years client-server systems have grown to include three or more tiers. These three tiers have also been referred to as front-end software, back-end software, and middleware (Burleson, 1994, p.79). Such layered architectures allow separate platforms for data storage, processing of data according to business rules, and user interface. This promotes code reuse and the ability to change or upgrade individual platforms while requiring little or no modification to the other layers.
The three-tiered client-server architecture promotes the implementation of new distributed database systems by limiting the impact of the changed database architecture on the application as a whole. Most commonly, the distributed database architecture can be changed without any modifications to workstation code since the middle tier handles all interface with the database. Such multi-tiered client-server systems have helped overcome the drawbacks of the increased cost of client-server systems by adding to the value they bring to the organization.