1. Data Base Administrator:
Centralized control of the Data base is exerted by a person or group of persons under the supervision of a high level administrator.
This person or group is referred to as the data base administrator (DBA).
They are the users who are most familiar with the data base and are responsible for creating, modifying and maintaining its three levels.
The DBA is the custodian of the data and controls the data base structure. The DBA administers the three levels of the data base and in consultation with the overall user community, sets up the definition of the global view or conceptual level of the data base.
The DBA further specifies the external view of the various users and applications and is responsible for the definition and implementation of the internal level, including the storage structure and access method to be used for the optimum performance of the DBMS.
Changes to any of the three levels necessitated by changes or growth in the organisation and/or emerging technology are under the control of the DBA. Mapping between the internal and the conceptual levels, as well as between the conceptual and external levels, are also defined by the DBA.
Ensuring that appropriate measures are in place to maintain the integrity of the data base and that the data base is not accessible to un-authorised users is another responsibility. The DBA is responsible for granting permission to the users of the database and stores the profile of each user in the data base.
This profile describes the permissible activities of a user on that portion of the data base accessible to the user via one or more user views. The user profile can be used by the data base system to verify that a particular user can perform a given operation on the data base
The DBA is also responsible for defining procedures to recover the data base from failures due to human, natural, or hardware causes with minimal loss of data. This recovery procedure should enable the organisation to continue to function and the intact portion of the data base should continue to be available.
2. On Line Users:
There are users who may communicate with the data base directly via an online terminal or indirectly via a user interface and application program. These users are aware of the presence of the data base system and may have acquired a certain amount of expertise in the limited interaction they are permitted with the data base through the intermediary of the application program.
The more sophisticated of these users may also use a data manipulation language to manipulate the data base directly. On line users can also be naive users requiring additional help, such as menus.
3. Naive Users:
Users who need not be aware of the presence of the data base system or any other system supporting their usage are considered naive users. A user of an automatic teller machine falls in this category. The user is instructed through each step of a transaction, he responds by pressing a coded key or entering a numeric value.
The operations that can be performed by this class of users are very limited and affect a precise portion of the data base; in the case of the user of the automatic teller machine, only one or more of her or his own accounts.
Other such naive users are end users of the data base who work through a menu oriented application program where the type and range of response is always indicated to the user. Thus, a very competent data base designer could be allowed to use a particular data base system only as a naive user.
4. Application Programmers:
Professional programmers who are responsible for developing application programs or user interfaces utilised by the naive and on line users fall into this category. The application program could be written in a general purpose programming language such as Assembler, C, COBOL, FORTRAN, Pascal or PL/1 and include the commands required to manipulate the data base.