Mainframes

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DBMS concepts

DBMS Basics

                       

            DataBase:- It’s a collection of records/data that is organized in such a way that

            It can easily be accessed, managed and updated.

           

            DBMS (Database Management System):- It’s software which is use to   

            Maintain the Database.

 

            DBMS structure:

             

             Application software ßàDBMSßàDatabase                      

                        

Before DBMS:  Before DBMS there is a FMS (File Management System) used to store data in a computerized database.

       The Data item is stored sequentially in one large file. There is no particular relationship can not be drawn between the Items other than the sequence in which it is stored.

        If a particular data item has to be located, the search starts at the beginning and Items are checked sequentially till the required Item is found.

 

Drawbacks of File-Based System:  

• Data Redundancy and Inconsistency

Since data resides in different private data files, there are chances of redundancy and resulting inconsistency. For example, in the above example shown, the same customer can have a savings account as well as a mortgage loan. Here the customer details may be duplicated since the programs for the two functions store their corresponding data in two different data files. This gives rise to redundancy in the customer's data. Since the same data is stored in two files, inconsistency arises if a change made in the data in one file is not reflected in the other.

• Unanticipated Queries

In a file-based system, handling sudden/ad-hoc queries can be difficult, since it requires changes in the existing programs.

• Concurrent Access Anomalies

In large multi-user systems the same file or record may need to be accessed by multiple users simultaneously. Handling this in a file-based systems is difficult.

• Security Problems

In data-intensive applications, security of data is a major concern. Users should be given access only to required data and not the whole database. In a file-based system, this can be handled only by additional programming in each application.

• Integrity Problems

In any application, there will be certain data integrity rules which needs to be maintained. These could be in the form of certain conditions/constraints on the elements of the data records. In the savings bank application, one such integrity rule could be “Customer ID, which is the unique identifier for a customer record, should be non-empty”. There can be several such integrity rules. In a file-based system, all these rules need to be explicitly programmed in the application program.