A database is a collection of related data. Data means, known facts that
can be recorded and that have implicit meaning.
A database management system (DBMS) is a collection of programs
that enables users to create and maintain a database. The DBMS is a
general-purpose software system that facilitates the processes of
defining, constructing, manipulating, and sharing databases among
various users and applications.
Defining a database involves specifying the data types, structures, and
constraints of the data to be stored in the data-base.
Constructing the database is the process of storing the data on some
storage medium that is con-trolled by the DBMS.
Manipulating a database includes functions such as querying the
database to retrieve specific data, updating the database to reflect
changes in the miniworld, and generating reports from the data.
Sharing a database allows multiple users and programs to access the
An application program accesses the database by sending queries or
requests for data to the DBMS. A query typically causes some data to be
retrieved; a transaction may cause some data to be read and some data
to be written into the database.
Other important functions provided by the DBMS include protecting the
database and maintaining it over a long period of time.
Protection includes system protection against hardware or software
malfunction (or crashes) and security protection against unauthorized or
A typical large database may have a life cycle of many years, so the
DBMS must be able to maintain the database system by allowing the
system to evolve as requirements change over time.