DATABASE MANAGEMENT SYSTEM



DATABASE MANAGEMENT SYSTEM

INTRODUCTION

Database management system is a collection of interrelated data and set of program to access those data. The collection of data, usually referred to as the database, contains information relevant to an interprise. The primary goal of dams is provide a way to store and retrieve database information that is both convenient and efficient.
Database system is designed to manage large body of information. Management of data involves both defining structure for storage of information and providing mechanism for the manipulation of information. Because information is so important in most organization, computer scientists he have developed have a large body of concept and techniques for managing data .

DATABASE SYSTEM APPLICATIONS:-

Database are widely used here are some representative  applications:

  1-BANKING- for customer information, account loan, and banking transactions

  2-AIRLINES- for reservations and schedule information .airlines were among the first to use database in a geographically distributed manner-terminal situated around the world accessed the central database system through phone lines and other data networks.

3-.UNIVERSITIES- for student information, course registration and grades.

 4-credit card transaction
 5-telecommunications
 6-finance
7-human resources
These are some applications of database management system

DATABASE SYSTEM VERSUS FILE SYSTEMS:-

Consider part of a saving-bank enterprise that keeps information about all customers and saving accounts.one way to keep information on computer is to store it in operating system files. To allow user to manipulate information, the system has a number of application program that manipulate the files, including
  .A program to debit or credit an account
 .a program to add a new account
 .A program to find the balance of an account
 .A program to generate monthly statements

System programmers wrote these programs to meet the need of the bank.

This typical file –processing system is supported by a conventional operating system. The system store permanent records in various files, and it needs different application program to extract record from, and add record to, the appropriate files. Before database management system (DBMSs) came along, organization usually stored information in such system.

Keeping organizational information in a file-processing system has a number of major disadvantages:

    1-data redundancy and inconsistency- same information may be duplicated in several places (files). For example, the address and telephone number of a particular customer may appear in a file that consist of at saving account record and in a file that consist of checking-account record. This redundancy leads to higher storage and access cost.in addition, it may lead to data inconsistency; that is the various copies of the same data may no longer agree.

2-DIFFICULTY IN ACCESSING DATA-suppose that one of the bank officers need to find out the name of all customer who live within a particular postal-code area. The officer say data-processing department to generate such a list 

3-DATA ISOLATION- because data are scattered in various files, and files may be in different format, writing new application program to retrieve the appropriate data is difficult.

4-INTEGRITY PROBLEM- data values stored in the database must satisfy certain types of consistency constraints. For example the balance of an account may never fall below a prescribed amount (say $25).developer enforce these constraints in the system by adding appropriate code in the various application programs. However when new constraints are added.it is difficult to change the program to enforce them

5-ATOMICITY PROBLEM- for example suppose transfer $50 from account A to B .but problem occur during execution time then $50  deducted from account A but not debited in account in B at that time so transaction should be  atomic

6-CONCURRENT-ACCESS ANOMALIES- for example suppose account A($500) access by two a/c X and Y withdraw $50 and $100 respectively  at the same time then in file show the two value $450 and $400 which  one  write first ,while actual $350.

7-SECURITY PROBLEM-Not every user of database system should be able to access all the data.

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