Database management systems are programs that are written to store, update, and retrieve information from a database. There are many databases management system available in the market. The most popular are the Oracle, SQL Server and MS Access. The Oracle database is from the Oracle Corporation, the SQL Server and MS Access is from the Microsoft Corporation. There are freely available database like My SQL, MS Access one of the best common and free user database. These are open source databases. Database Management Systems are available for personal computers and for huge systems like mainframes. DB2 is a database from IBM for Mainframe systems.
Function of Database
User databases also permit you to set up rules that ensure that data remains consistent when you add, update, or delete data. Suppose that your computer sales Organization have two salesmen named David. You can set up a database to ensure that each salesmen has a unique ID, so that can not be mixed up between them, otherwise, telling who sold which computer would not be possible. Other data storage systems, like text files or spreadsheets, don't have these sorts of checks and quite happily allow you to store erroneous data that is not much useful in compare to database.
For example, you might specify that an employee's social security number must be unique in the database. Or if a computer is sold and it's listed as being sold by the employee with an ID of 00234, you might add a check to see that full details of employee 00234 are held in one of the database tables.
You can share data among a number of users on the same computer or among users on different computers linked via a network or the Internet. If the example computer sales organization has branches in Washington, Philadelphia, Chicago and Boston, you could set up a computer containing a database in one location that is accessible by all of the offices via a network. This is not only possible but also safe because databases have a clearly defined structure and also enforce rules that protect the data contained. They also allow more than one database manager to access the database at the same time and change the data stored, the database management system handles simultaneous changes too.