Computer File Processing System:
Before understanding the characteristics of a pure database system, it is
necessary to know about the computer file processing system. Computer file processing system is still used in the environments where computers are used but there is no DBMS.
In such systems, the data is usually kept through computer files on magnetic
disk or tape. Data is stored and managed in data files through application programs. Each department (or user) defines and implements the data files needed
for different tasks. Each application program is developed with its own set of
data files to meet the needs of a particular department.
Example:
For example, the admission office of a college may have an application program
for maintaining records of candidates for admission in the college. The
admission office forwards information about the enrolled students to the head of
the department (or dean or registrar). If the information of students/candidates
are collected in the form of printed reports, then these must be re-entered into
the computer. Similarly, the registrar's office "owns" not only its file of
current students, but also may have files concerning courses offered, schedules,
and so on. The dean's office may have its own students file, course file, as
well as faculty file. Faculty information is also kept by each department, for use in payroll and other applications. In each case, all departments or offices have their own data files. The departments/offices of the university share the information by copying data files on disk or by obtaining printout with the permission of the owner, A traditional computer file processing system of a university is shown in figure 1.3.
In the above diagram:
- "Student.dat" data file created and maintained in admission office is used
with "Admission" program to create the data file and to generate the list of
successful candidates. This file is also forwarded to registrar's office.
- "Course.dat" data file created in registrar's office contains information
about courses of different subjects. This file and "student.dat" file are used with "Schedule" program to generate individual student schedules and class
lists.
- The "pay.dat" data file has information required for calculating pay to
prepare payroll sheets. The "pay.dat" file is used in "Payroll" application
program. It is used to create payroll of the employees.
Disadvantages of Computer File Processing
System:
Although a computer file processing system has many advantages over the manual
record keeping system, but it has some limitations also. The basic
disadvantages (or limitations) of computer file-based system are described
below:
1. Data Redundancy:
Data redundancy means multiple copies of the same data. In computer file-based
system, each application program has its own data files. The same data may exist
in more than one file. The duplication of data creates many problems, such as:
(i) To update specific data/record. The same data must be updated in all the
files; otherwise different files may have different information about a specific
record.
(ii) A valuable storage space is wasted due to duplication of records.
For example, in the university environment, admission office creates the
"student.dat" data file. This file contains the information of students such as
roll numbers, names, and addresses etc. Similarly, the registrar's office
creates file "result.dat", which contains information of students such as roll
numbers, names, addresses, obtained marks of subjects, .and results of all the
examinations etc. In this case, both files contain the roll numbers, names, and
addresses of the students. The same data of students is stored in multiple
files. This is known as data redundancy.
2. Data Inconsistency:
Data inconsistency means that different files contain different information of a
particular object or person. Actually redundancy leads to inconsistency. When
the same "data is stored at multiple locations, the inconsistency occurs. For
example, suppose the address of a student is changed and it is updated in the
data file located at registrar's office only. Since, the data files are
maintained by other departments also, therefore some data files may contain the
old address, while others contain the new address. Thus data inconsistency
arises because of partial updating of student's address.
3. Data Isolation:
In computer file-based system, data is isolated in separate files. It is difficult to access the desired information from data files. For example, if the addresses of students are stored in the data file "student.dat" and examination marks of students are stored in the data file "result.dat" and now you need data from both files. With computer file processing, it is a difficult job. The
programmer must change the data files to extract the required data. In such
systems, it is very difficult to merge required data from two or more data
files.
4. Data Atomicity:
One complete operation carried out on a database is called a transaction. An
operation (or transaction) on a database may consist of more than one task.
Atomicity means that either one transaction should take place as a whole or it
should not take place at all. For example, in case of computer file processing
system, the names of students who have paid their fees is maintained in one file
and the names of students who have not paid their fees is maintained in another
file. If a student has paid his fee, his name is entered in the file that
contains the names of students who have paid their fees. It is possible that,
for some reasons, the name of student is not removed from the file that contains
the names of the students who have not paid their fees. Thus the name of the
student will appear in both the data files and the data will become
inconsistent. This is called the data atomicity problem. This problem usually
occurs in computer file processing systems.
5. Program Data Dependency:
In these systems, the data stored in a file depends upon the application program
through which the file was created. It means that the structure of the data file
is coupled with its application program.
The physical structure of data files, and records is defined in the application
program. It is difficult to change the structure of data files or records. If
you want to change the structure of data file (or format of file), then you have
to modify the application program. This characteristic of file-based systems is
known as program-data dependency.
6. Difficult Program Maintenance:
In computer file-based systems, the structure of data file is coupled with the
application programs. Therefore, any modification in a data file (such as size
of data field, its data type etc.) requires the redesigning of the application
program also. In this case, you have to spend a lot of time for modifying,
testing and debugging the program. If an organization has an application program
developed by a software company, then has to pay a lot of money for the
maintenance of the programs.
7. Limited Data Sharing:
In computer file processing systems, each application program uses its own
private data files. The computer file processing systems provide the limited
facility to share data of a data file among multiple users on the network.
8. Data Insecurity:
The computer file processing systems do not provide proper security against
illegal access to data. Any one can easily change or delete valuable data stored
in the data file. It is the most critical problem of a file processing system.
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