Database Management System

A database management system (DBMS) is a set of program that allows the creation of datafile, the alteration of the data in these files and the extraction of date from the files. The idea with a DBMS is that all the data is kept centrally and only authorized system can access data via the DBMS.

All database management systems allow the following:

• data files to be set up by creating tables (or datafiles) which may be linked together
• users to ask queries of the data e.g search for data meeting certain criteria
• addition of more data (appending), deletion and editing of existing data
• alteration to the structures of the datafiles or tables
• security by allowing only certain people access to each of the datafiles or tables
• user to import data into the database from other packages and data to be transferred to another package (exporting)

File Organization

There are several methods to organize file.

• Serial Files: Here records don't follow each other in any particular order, if another record needs to be added it can just be added to the end of the file.

• Sequential Files: They are like serial files except the the records are held in a certain sequence e.g to order pupil file in admission number sequence

• Random Files: Random files have to be stored on disk and they are not stored in any order on the disk surface. The disk operating system keeps a map of the disk surface and using this map the read/write heads can go straight to the data. In this way, the data is found without the whole disk having to be read. Random access allows data stored on disk to be found extremely quick.