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What is a file-processing system? What are the disadvantages of a file-processing system that led to the development of the database system?

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In the file-processing system, the data are stored in the form of files, and a number of application programs are written by programmers to add, modify, delete and retrieve data to and from appropriate files. New application programs are written as and when needed by the organization. For example, consider a bookstore that uses a file-processing system to keep track of all the available books. The system maintains a file named BOOK to store the information related to books. This information includes the book title, ISBN, price, year of publishing, copyright date, category, number of pages, name of the author and the name and address of the publisher.

In addition, the system has many application programs that allow users to manipulate the information stored in the BOOK file. For example, a system may contain programs to add information about a new book, modify any existing book information, print the details of books according to their categories, etc. If a need arises to keep additional information about the publishers of the books, which include the phone number and email id, the system creates a new file, say PUBLISHER, which includes the name, address, phone number and email id of the publishers. New application programs are written and added to the system to manipulate the information in the PUBLISHER file. In this way, as time goes by, more files and application programs are added to the system.

The file-processing system has a number of disadvantages that lead to the development of database systems. These disadvantages are given below:

  • Same information may be duplicated in several files. For example, the name and the address of the publisher are stored in the BOOK file as well as in the PUBLISHER file. This duplication of data is known as data redundancy, which leads to wastage of storage space. The other problem with the file-processing system is that the data may not be updated consistently. Suppose a publisher requests for a change in his address. Since the address of the publisher is stored in the BOOK as well as the PUBLISHER file, both the files must be updated. If the address of the publisher is not modified in any of the two files, then the same publisher will have different addresses in two different files. This is known as data inconsistency.
  • In any application, there are certain data integrity rules that need to be maintained. These rules could be in the form of certain conditions or constraints. In a file-processing system, all these rules need to be explicitly programmed in all application programs that use that particular data item. For example, the integrity rule that each book should have a book title has to be implemented in all the application programs separately that use the BOOK file. In addition, when new constraints are to be enforced, all the application programs should be changed accordingly.
  • The file-processing system lacks the insulation between program and data. This is because the file structure is embedded in the application program itself; thus, it is difficult to change the structure of a file as it requires changing all the application programs accessing it. For example, an application program in C++ defines the file structure using the keyword struct or class. Suppose the data type of the field ISBN is changed from string to number, changes have to be made in all the application programs that are accessing the BOOK file.
  • Handling new queries is difficult, since it requires change in the existing application programs or requires a new application program. For example, suppose a need arises to print the details of all the textbooks published by a particular publisher. One way to handle this request is to use the existing application program that prints the details of the books according to their categories, and then manually generate the list of textbooks published by a particular publisher. Obviously, it is unacceptable. Alternatively, the programmer is requested to write a new application program. Suppose such a new application program is written. Now suppose after some time, a request arises to filter the list of textbooks with a price greater than $50. Then again we have to write a new application program.
  • Since many users are involved in creating files and writing application programs, the various files in the system may have different file structures. Moreover, the programmers may choose different programming languages to write application programs.
  • Since application programs are added in an unplanned manner, due to which the details of each file are easily available to every user. Thus, the file-processing system lacks the security feature.