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Request

                                        Information
                                                                                        Database
                                                              DBMS          Data
                                              Request        Software


                                          Information

                                               Fig 9.2: User interface with DBMS software

            9.1.2 Need for DBMS
            In the olden days, the data was managed manually in registers or as papers in files. Related files were physically placed
            in folders, and folders were organised in cupboards or wardrobes. If we wish to manage all the information about a
            company manually, we would need separate file folders to maintain data about employees, departments, projects, etc.
            The data about an employee would be typically fragmented in several files. Further, there may be multiple copies of
            the same data in different files. For example, an employee's leave record may be maintained by the local office and the
            head office. Similarly, the human resources (HR) department and the accounts department may maintain their copies
            of the salary payable to the employees. Multiple copies of the same data will lead to the possibility of inconsistency
            in data as it may not be possible to apply updates to all copies of the data simultaneously. Thus, as data increases,
            ensuring the consistency of data becomes cumbersome.
            Over time, manual file systems were replaced by computerised file systems. Searching or modifying data became much
            faster in these systems. Based on the computerised file systems, various information systems were developed to meet
            the requirements of businesses. However, these systems were also plagued with the problem of data redundancy
            because they still contained multiple copies of the same data. Data redundancy leads to the following problems:

            1. Wastage of Storage Space: The Same data appears at various places.
            2.  Increased Data Processing Effort: An update operation involving a data item that appears in several files requires
               updating all those files. For example, if an employee's salary is updated, all the files containing information about
               the employee's salary will have to be updated.
            3.  Inconsistent Data: While updating data, it may happen that one file correctly reflects updated data whereas the
               other file still contains old data or incorrectly updated data. For example, suppose an employee's salary needs to
               be increased by 3500. Using a conventional file system, a programmer may carry out the update correctly in the
               file relating to the accounts department. But the salary mentioned in a file in the HR department may not have
               been updated. There could be another situation that the salary in the HR department's file might be  increased
               by only 3000 because an incorrect version of the data file was used for the update. This kind of anomaly is quite
               likely to happen if different individuals are responsible for updating the same data at multiple places.
            Apart from data redundancy, computerised file systems have several other disadvantages as mentioned below:

            1.  Structural Data Dependence: A change in the structure of a file may require changes in the applications programs
               that use this file. For example, the inclusion of a new attribute email-id in a file containing employee data will lead to
               changes in the programs that use the employee file. Similarly, a  change in data characteristics, such as  an increase
               in the length of the address line, will affect other programs that use the employee file. Thus, application programs
               become dependent on the file structure.
            2.  Lack of Controls: Typically, organisations enforce a hierarchical system for defining access rights of different categories
               of users. For example, while the head of the EDP department may access all or most of the information available
               in an organisation, the head of the HR department, staff of the HR department, head of the accounts department,
               and accounts clerk will have restricted access to data. It is hard to enforce rules for authorising legitimate access to
               data in applications developed using conventional file systems.


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