Introduction to DBMS

 


Introduction to DBMS


The database is now such an integral part of our day-to-day life that often we are not aware we are using one. To start our discussion of databases, in this section we examine some applications of database systems. 

For the purposes of this discussion, we consider a database to be a collection of related data and the Database Management System (DBMS) to be the software that manages and controls access to the database. 

A database application is simply a program that interacts with the database at some point in its execution. We also use the more inclusive term database system to be a collection of application programs that interact with the database along with the DBMS and database itself.

Some examples of database



Purchases from the supermarket

When you purchase goods from your local supermarket, it is likely that a database is accessed. The checkout assistant uses a bar code reader to scan each of your purchases. This is linked to an application program that uses the bar code to find out the price of the item from a product database. The program then reduces the number of such items in stock and displays the price on the cash register. If the reorder level falls below a specified threshold, the database system may automatically place an order to obtain more stocks of that item. If a customer telephones the supermarket, an assistant can check whether an item is in stock by running an application program that determines availability from the database.


Purchases using your credit card

When you purchase goods using your credit card, the assistant normally checks that you have sufficient credit left to make the purchase. This check may be carried out by telephone or it may be carried out automatically by a card reader linked to a computer system. In either case, there is a database somewhere that contains information about the purchases that you have made using your credit card. To check your credit, there is a database application program that uses your credit card number to check that the price of the goods you wish to buy together with the sum of the purchases you have already made this month is within your credit limit. When the purchase is confirmed, the details of the purchase are added to this database. The application program also accesses the database to check that the credit card is not on the list of stolen or lost cards before authorizing the purchase. There are other application programs to send out monthly statements to each cardholder and to credit accounts when payment is received.

Booking a holiday at the travel agents

When you make inquiries about a holiday, the travel agent may access several databases containing holiday and flight details. When you book your holiday, the database system has to make all the necessary booking arrangements. In this case, the system has to ensure that two different agents do not book the same holiday or overbook the seats on the flight. For example, if there is only one seat left on the flight from London to New York and two agents try to reserve the last seat at the same time, the system has to recognize this situation, allow one booking to proceed, and inform the other agent that there are now no seats available. The travel agent may have another, usually separate, database for invoicing.


Using the local library

Your local library probably has a database containing details of the books in the library, details of the readers, reservations, and so on. There will be a computerized index that allows readers to find a book based on its title, or its authors, or its subject area. The database system handles reservations to allow a reader to reserve a book and to be informed by mail when the book is available. The system also sends reminders to borrowers who have failed to return books by the due date. Typically, the system will have a bar code reader, similar to that used by the supermarket described earlier, which is used to keep track of books coming in and going out of the library.

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