DBMS and RDBMS

A Database Management System (DBMS) is software that lets users create, store, organise, retrieve, update and manage the data in a database. It sits between the user (or an application program) and the actual data stored on disk, and it takes care of all the low-level details of how the data are physically kept. The user simply asks the DBMS for what they want — 'show all customers from Cuttack', 'add a new product', 'change this price' — and the DBMS carries out the request safely and efficiently.

A DBMS performs several important functions:

• Data definition — defining the structure of the data: what tables exist, what columns each table has, and what type of data each column holds.
• Data storage and retrieval — storing the data on disk and fetching exactly the records the user asks for, without the user needing to know where or how they are physically stored.
• Data manipulation — inserting new data, updating existing data, and deleting data that is no longer needed.
• Data security — controlling who is allowed to see or change which data, using user names, passwords and permissions.
• Data integrity — enforcing rules so that only valid, consistent data is stored (for example, that a marks column cannot hold a negative value).
• Backup and recovery — protecting data against loss by supporting backups and restoring the database to a correct state after a failure.
• Concurrent access control — allowing many users to work with the same database at the same time without their changes clashing or corrupting each other.

Why a DBMS is better than the older file-based system. In the file-based system each program kept its own separate data files, which caused several problems: data redundancy (the same fact, such as a customer's address, stored in many files, wasting space); data inconsistency (an update made in one file but not the others, so the files disagree); weak security (hard to control access to scattered files); and difficulty in sharing and querying (a new report often needed a whole new program). A DBMS overcomes these with controlled redundancy, consistency, central security, enforced data integrity, easy sharing and querying (through a language such as SQL) and organised backup and recovery. …