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.The back end is the set of related database tables—and in some cases, the database engine that serves as the interface between the front end and the tables.The terms client and server are sometimes used instead of front end and back end.Why bother with this separation between the front and back ends of a database? Why not just combine all database functionality into a single application? The answers to these questions is clear if you consider how most organizations use a database.An organization’s various databases cover a wide range of information—personnel records, salary information, sales data, inventory information, and so on.The various users within the organization, however, need to access selected subsets of this information in specific ways.The personnel department, for example, requires access to the personnel data and needs to look at information such as Social Security contributions and medical insurance payments.The shipping department has no use for personnel information (and may even be denied access to it), but shipping does need to view sales and inventory data.If the front and back ends of the database were combined in a single application, a single application would have to cover the needs of all potential users.It would be unavoidably large, complex, and cumbersome—not to mention difficult to customize for new or changed needs of a specific group of users.Additionally, and perhaps even more importantly, maintaining database integrity and validity would become a nightmare.The front end/back end approach avoids most of these problems.Each group of users can be given its own specialized software that is designed to do just what the group needs it to do, and nothing more.With a single program—the back end’s database engine—coordinating all access to the actual database files, matters of integrity and validity can be dealt with more easily, and controlling access to different parts of the database becomes feasible.Database front ends fall into two categories:• Decision–support applications—Enable users to view and query information in the database, but do not permit them to add or modify information.• Transaction–processing applications—Include the capability to add, delete, and edit data in the database.Decision–support applications, which vary widely in scope, are the most common type of database front end.This type of program can be extremely specialized and limited—for example, an application that displays only client and sales information can be designed for sales personnel.These programs can also be extremely flexible, as in complex management–information systems (MIS) that provide summary data on all information in a company’s database.Decision–support applications generally have read–only access to the database files—that is, they can read the data but can’t change it.Two approaches, often combined, can be taken toward the design of decision–support applications.Users can be given one or more fixed, nonmodifiable ways of examining the data, or they can be given the capability to design custom queries and reports.The former method has the advantage of requiring less training of the final users, but productivity suffers if the program’s predefined capabilities aren’t closely matched to the users’ needs.Transaction–processing applications provide the capability to add new data to a database and to edit or delete existing data.Because a transaction–processing application can change the actual table data, some additional programming considerations come into play.The application has the responsibility of preserving the integrity, or accuracy, of the data in the tables.Many databases are client/server databases.The terms client and server are being used somewhat differently here than they were earlier in the chapter, although it is still related to the concept of front end and back end.A client/server database refers to a multiuser database, to which multiple front ends are connected from different computers scattered around an organization.The client computers are connected via a network to the server computer on which the database back end is located.Multiuser client/server databases present some special problems, which are dealt with in Chapter 24.PreviousTable of ContentsNext | | | | | Use of this site is subject to certain ,All rights reserved.Reproduction whole or in part in any form or medium without express written of EarthWeb is prohibited.Read EarthWeb's privacy statement [ Pobierz całość w formacie PDF ]
