File Processing System

 Topic Outline

  • File Processing System
  • Types of File Organization
    • Sequential File Organization
    • Indexed File Organization
    • Direct File Organization
  • Disadvantages of File Processing System
    • Data Redundancy
    • Data Inconsistency
    • Data Integrity Problems
    • Atomicity Problem
    • Security Problem
    • Program Maintenance
    • Program Data Dependency


File Processing System

In the past days, organizations stored data in a file on disk or tape. In a file processing system, each department in an organization or institution has its own set of files. Files are designed for their own applications. Records in one file are not matched to the records in other files. Data were managed by using a file processing system. Business organizations and different institutions have used file processing systems for many years.


 


Types of File Organization

(1) Sequential File Organization

Records in sequential file organization are accessed sequentially. Records are stored one after the other. Records are accessed in the same sequence in which they are stored in the file. In sequential files, organization records are stored in ascending order and descending order. So this order is based on a value. Value is also called a key. A key is a field that contains unique data.

  • It's very slow.
  • If the last record is to be accessed all preceding records are read before reading the last record.

(2) Indexed File Organization

Records are stored in ascending and descending order. Index file organization maintains an index in a file. Index refers to the place where the record is stored. When a record is added or deleted from the file, then the index file is updated. The index consists of key values and disk addresses. Records can be accessed sequentially as well as random access in indexed file organization. 

  • Random access

It means records can be accessed directly without reading all records. Random access is faster than sequential access.

(3) Direct File Organization

The key value of the record is used to determine the location to store the record. A program establishes a file that has seven locations to store records. If the key in the record is one digit value, this value can be used to identify the location to store that record.

Example

The record with key 6 can be stored at relative location 4 and so on. A relative location is also called a bucket.

If the maximum number of records to be stored is 100 and key for a record four-digit number. Four-digit kay can give results up to 9999. So key cannot be used to identify the access location. A formula can be used to find relative location. This method is called hashing.

Disadvantages of File Processing System

  • Data Redundancy

Data redundancy means the duplication of data in several files. 

Example

Suppose there are two files "students" and "fees". The file "students" contain roll no, name, address, phone number, department, and other information of all students in a university. The file "fees" contains the roll no, name, and department of those students who pay fees. The data of one student appears in two files. This is known as redundancy.

  • Data Inconsistency

Inconsistency means two files have different data of the same student.

Example

If the roll no of a student is changed, it must be changed in both files. There is a possibility, it is changed in the "student" file and not changed from the "fees" file. In this situation data becomes inconsistent.

  • Integrity Problems

It means reliability and accuracy of data. Stored data must satisfy certain types of consistency constraints.

Example

Roll no and Registration no of students should be in numeric value. In the file operating system, it is difficult to apply these constraints to files.

  • Atomicity Problem

It means that either one transaction should take place as a whole or should not take place at all. When we apply any operation on data, it may consist of different steps. A user wants to transfer money from account A to B.

Steps

  • Deduct the money from account A.
  • Add the money to account B.

If the system fails when the computer has performed the first step. It means the money has been deducted from account A but has not been added to account B.

  • Security Problems

It does not provide adequate security on data. 

Example

The data entry operator should only be able to enter data. The Chairman of any organization or institution should only be able to access or delete the data.

  • Program Maintenance

It is very difficult to maintain the developed program and develop a new program in the file processing system. Most budget is spent on its maintenance.

  • Program Data Dependency

Application programs are developed according to a specific file format. If the file format is changed, the application program also needs to be changed. The changes may be costly to apply.



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