Mumbai University > Information Technology > Sem 3 > Database Management System

Marks: 10M

Year: Dec 2014

1. Introduction

• In a typical file processing system, each and every subsystem of the information system will have its own set of files.
• The typical file-oriented system is supported by a conventional operating system. Permanent records are stored in various files and a number of different application programs are written to extract records from and add records to the appropriate files.
• Disadvantages of file system include:
  • Data redundancy and inconsistency
  • Difficulty in accessing data
  • Concurrent access anomalies
  • Security problem
  • Integrity problems
  • Data isolation

1. Advantages of DBMS over file system

• Redundancy can be reduced:

  A major difficulty was that many applications used their own special files of data. Thus, some data items were common to several applications. For example address and phone number of particular customer may appear in a file that consists of personal information and savings account also. This redundancy leads to higher storage and access costs. Database systems can eliminate data redundancy, since all applications share a common pool of data. Essential information such as customer name will appear just once in the database.

• Inconsistency can be avoided:

  Since the same information can be present at multiple files in file systems, data needs to be updated at all the files whenever any changes in data occur. For example, a changed customer address may be reflected in personal information file, but not in savings account file. By having a centralized database, most of this can be avoided.

• Reduced programming effort:

  A new application program often required an entirely new set of file definitions. Even though an existing file may contain some of the data needed, the application often required a number of other data items. As a result, the programmer had to recode the definitions of needed data items from the existing file as well as definitions of all new data items. Thus, in file-oriented systems, there was a heavy interdependence between programs and data. Database provides a separation between programs and data, so that programs can be somewhat independent of the details of data definition. By providing access to a pool of shared data and by supporting powerful data manipulating languages, database systems eliminate a large amount initial and maintenance programming.

• Security can be enforced:

  Not every user should be able to access all the data. For example, in a banking system, payroll personnel need only the information about various bank employees. They do not need access to customer accounts. Since, in the file systems, application programs are added to systems in ad-hoc manner, it is difficult to enforce security constraints. With central control over the database, the DBA (Database Administrator) can define the access paths for accessing the data stored in the database and he can define authorization checks whenever access to sensitive data is attempted.

• Integrity can be maintained:

  The data values stored in the database must satisfy certain types of consistency constraints. For example, the balance of a bank account may never fall below a particular amount. In file system, these constraints are enforced by adding appropriate code in various application programs. However, when new constraints are added, it is difficult to change the programs to enforce them.

  Centralized control of the data helps in permitting the administrator to define integrity constraints to the data in the database.