database management system

database (DBMS) A suite of programs which typically manage

large structured sets of persistent data, offering ad hoc

query facilities to many users. They are widely used in

business applications.

A database management system (DBMS) can be an extremely

complex set of software programs that controls the

organisation, storage and retrieval of data (fields, records

and files) in a database. It also controls the security and

integrity of the database. The DBMS accepts requests for data

from the application program and instructs the operating

system to transfer the appropriate data.

When a DBMS is used, information systems can be changed much

more easily as the organisation's information requirements

change. New categories of data can be added to the database

without disruption to the existing system.

Data security prevents unauthorised users from viewing or

updating the database. Using passwords, users are allowed

access to the entire database or subsets of the database,

called subschemas (pronounced "sub-skeema"). For example, an

employee database can contain all the data about an individual

employee, but one group of users may be authorised to view

only payroll data, while others are allowed access to only

work history and medical data.

The DBMS can maintain the integrity of the database by not

allowing more than one user to update the same record at the

same time. The DBMS can keep duplicate records out of the

database; for example, no two customers with the same customer

numbers (key fields) can be entered into the database.

Query languages and report writers allow users to

interactively interrogate the database and analyse its data.

If the DBMS provides a way to interactively enter and update

the database, as well as interrogate it, this capability

allows for managing personal databases. However, it may not

leave an audit trail of actions or provide the kinds of

controls necessary in a multi-user organisation. These

controls are only available when a set of application programs

are customised for each data entry and updating function.

A business information system is made up of subjects

(customers, employees, vendors, etc.) and activities (orders,

payments, purchases, etc.). Database design is the process of

deciding how to organize this data into record types and how

the record types will relate to each other. The DBMS should

mirror the organisation's data structure and process

transactions efficiently.

Organisations may use one kind of DBMS for daily transaction

processing and then move the detail onto another computer that

uses another DBMS better suited for random inquiries and

analysis. Overall systems design decisions are performed by

data administrators and systems analysts. Detailed database

design is performed by database administrators.

The three most common organisations are the hierarchicaldatabase, network database and relational database. A

database management system may provide one, two or all three

methods. Inverted lists and other methods are also used. The

most suitable structure depends on the application and on the

transaction rate and the number of inquiries that will be

made.

Database machines are specially designed computers that hold

the actual databases and run only the DBMS and related

software. Connected to one or more mainframes via a

high-speed channel, database machines are used in large volume

transaction processing environments. Database machines have a

large number of DBMS functions built into the hardware and

also provide special techniques for accessing the disks

containing the databases, such as using multiple processors

concurrently for high-speed searches.

The world of information is made up of data, text, pictures

and voice. Many DBMSs manage text as well as data, but very

few manage both with equal proficiency. Throughout the 1990s,

as storage capacities continue to increase, DBMSs will begin

to integrate all forms of information. Eventually, it will be

common for a database to handle data, text, graphics, voice

and video with the same ease as today's systems handle data.

See also: intelligent database.

(1998-10-07)