One of the main reasons for using DBMSs is to have central control of both the data and the programs that access those data. A person who has such central control over the system is called a database administrator (DBA). The functions of a DBA include:
Schema definition. The DBA creates the original database schema by executing a set of data definition statements in the DDL.
Storage structure and access-method definition. Schema and physical-organization modification. The DBA carries out changes to the schema and physical organization to reflect the changing needs of the organization, or to alter the physical organization to improve performance.
Granting of authorization for data access. By granting different types of authorization, the database administrator can regulate which parts of the database various users can access. The authorization information is kept in a special system structure that the database system consults whenever someone attempts to access the data in the system. Routine maintenance. Examples of the database administrator’s routine maintenance activities are:
Periodically backing up the database, either onto tapes or onto remote servers, to prevent loss of data in case of disasters such as flooding.
Ensuring that enough free disk space is available for normal operations, and upgrading disk space as required.
Monitoring jobs running on the database and ensuring that performance is not degraded by very expensive tasks submitted by some users.