Database Management System (DBMS)

DBMS Features

Many examples of databases are familiar from everyday life, such as the database you might use to search for a book in your local library or the database a bank uses to store information about its customers' bank balances and transactions. The software used to store, manage, and retrieve the data in these databases is a DBMS. All DBMS, regardless of the application [Page 70]for which they are used, share a number of common features.

A defining feature of a database is that it is computationally efficient. Efficiency requires that a DBMS be able to operate at high performance, storing and retrieving information very rapidly. Normally, a DBMS operates so fast that the responses appear to be nearly instantaneous. Efficiency also helps to ensure that a DBMS is scalable, able to store anything from a few dozen to a few million records.

A second feature of a DBMS, termed data independence, is that users should be able to access data independently of the technical details of how data are actually stored in the DBMS. For example, a user who wants to search for a book in a library should be able to do so without knowing anything about how, where, or in what format these data are stored inside the DBMS. As a result of data independence, it should be possible to add and delete data, change the computer used to store the data, or even change the DBMS itself without changing the way users access that data.

A third feature is that a DBMS should be able to enforce logical constraints and relationships between data items stored in the database. For instance, if a bank database stores information about the current balances of its customers, the DBMS should be able to prevent any data other than numbers being entered as balances. Similarly, if data about a withdrawal from a particular account are to be stored in the database, the DBMS must prevent invalid account numbers being entered, such as account numbers that do not refer to current customers of that bank. In this way, a DBMS protects the integrity of the data.

Fourth, a DBMS should be able to describe the structure of the data in its database. So, in addition to asking questions about the data itself, database administrators should be able to ask the DBMS questions about what sorts of data the database contains. For example, in a bank database, we would expect the DBMS to be able to tell us that it stores information about the addresses of customers, as well as answering questions about the actual addresses of specific customers.

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