Page 101 - DCAP516_COMPUTER_SECURITY

Unit 8: Introduction to Databases

3. Be usable by all the programs Notes
4. Include all the necessary structural interrelation of data.

8.9 Purpose and Need

A file system is one in which we keep the information in operating system files. Before the
evolution of DBMS, organisations used to store information in file systems. A typical file
processing system is supported by a conventional operating system. The system stores permanent
records in various files and it need application program to extract records, or to add or delete
records. We will compare both systems with the help of an example. Suppose, there is a saving
bank enterprise that keeps information about all customers and saving accounts. The following
manipulations have to be carried out within the system:

1. A program to debit or credit an account.
2. A program to add a new account.
3. A program to ascertain the balance of an account.
4. A program to generate monthly statements.
As the need, arises new applications can be added at a particular point of time as checking
accounts can be added in a saving account.

8.10 Disadvantages

Using file system for storing data has got following disadvantages:
1. Data Redundancy and Inconsistency: Different programmers work on a single project, so
various files are created by different programmers at some interval of time. So various
files are created in different formats and different programs are written in different
programming languages. The same information is repeated. For example, name and
address may appear in saving account file as well as in checking account. This redundancy
results in higher storage space and access cost. It also leads to data inconsistency, which
means that if we change some record in one place, the change will not be reflected in all
the places. For example, a changed customer address may be reflected in saving record but
not anywhere else.

2. Difficulty in Accessing Data: Accessing data from a list is also a difficulty in file system.
Suppose, we want to see the records of all customers who have a balance of less than
` 10,000, we can either check the list and find the names manually or write an application
program. If we write an application program and at some later time, we need to see the
records of customers who have a balance of less than ` 20,000, then again a new program
has to be written. It means that file processing system do not allow data to be accessed in
a convenient manner.
3. Data Isolation: As the data is stored in various files, and various files may be stored in
different format, writing application program to retrieve the data is difficult.
4. Integrity Problems: Sometimes, we need that data stored should satisfy certain constraints,
as in a bank a minimum deposit should be of ` 100. Developers enforce these constraints
by writing appropriate programs, but if later on, some new constraint has to be added
then it is difficult to change the programs to enforce them.
5. Atomicity Problems: Any mechanical or electrical device is subject to failure, and so is the
computer system. In this case, we have to ensure that data should be restored to a consistent

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