Explanation of a Database Management System
May 20, 2009
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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.
1. Application program instruction initiates a request for data
2. Control unit transfers control to DBMS
3. DBMS verifies that the request is valid and determines location of data element in database
4. DBMS issues command to access data from secondary storage
5. Data element is accessed and stored in a buffer of the DBMS
6. DBMS transfers data element to application program storage area
7. Next instruction in application program is accessed and executed
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