In addition to the data itself, a set of
program is necessary to facilitate adding new data as well as modifying and
retrieving existing data within a database. This set of programs is referred to
as database management system (DBMS).
Generally, the user of a database management
system accesses the database via a special query language or via applications
programs written in a high-level language. The applications program utilizes
special host- or command-language instructions to communicate requests for data
to the portion of the DBMS referred to as the database processing system.
Basically, the database processing system consists of a series of programs that
translate requests from users or user programs into the instructions necessary
to access, add to, change, or delete records or items of data from database.
Thus, an applications program need include only a command to access the desired
data element. The actual mechanics of locating and accessing the data element
are accomplished by the database processing programs.
Accessing Data from a database in response to
an applications program request.
- Application program instruction initiates a request for
- Control unit transfers control to DBMS
- DBMS verifies that the request is valid and determines
location of data element in database
- DBMS issues command to access data from secondary
- Data element is accessed and stored in a buffer of the
- DBMS transfers data element to application program
- Next instruction in application program is accessed and