Database systems have become an essential part of everyday life in modern society. Most of us encounter several activities that involve some interaction with databases. For example if we go to a bank to deposit or withdraw money or if we make a hotel or airline reservations or if we access a computerized library catalog to search for a book , chances are that our activities will involve some kind of database. Even purchasing items from a supermarket in many cases involves an automatic update of the database that keeps the inventory of supermarket items. Everyday we are search internet for different purposes using search engines like Google. In fact every search engine also has a database working on the back end. Every organization has to maintain record of its employees so every company regardless of size has to maintain an efficient database.

A database is a collection of related data. By data I mean raw facts and figures that can be recorded and that have implicit meaning. For example, consider the names, telephone numbers and address of the people you know. You may have recorded this data in a indexed address book or you may have stored it on a disk, using a personal computer and a software such as Microsoft Access or Microsoft Excel. This is a collection of data with an implicit meaning and hence is a database.

All the data belonging to an organization is centralized in a common pool of data, accessible by all applications. A database can be of any size or complexity. For example List of name and addresses may contain only a few hundred records, each with a simple structure. On the other hand a large library database may contain half a million records with greater size and complexity. Back in the days there were two approaches to maintain a database, manually or computerized. The library card catalog is an example of database that may be created and maintained manually. A modern database is created by a team of database designers, DBMS certified professionals and application developers. And modern database is maintained by a professional called Database Administrator DBA.