Database Management System

A file system stores data in separate, unrelated files. This creates several problems: data redundancy (the same data repeated in many files), data inconsistency (conflicting copies of the same data), difficulty in accessing related data, and no built-in way to enforce rules or share data safely among multiple users. A database solves these problems by storing data in a single, logically connected collection.

A database is an organised collection of logically related data. The software that creates, manages, and controls access to this database is called a Database Management System (DBMS) — often shortened to database system. The DBMS acts as the middle layer between the raw data on disk and the end users or application programs that need that data.

What a DBMS Does

A DBMS lets users and programs perform all essential operations on a database:

• Create a new database and define its structure (tables, columns, relationships).
• Store data into that structure.
• Manage the data — update it, modify it, and delete it.
• Retrieve data on demand, either for a single user or for an application.

The act of retrieving data from a database using special commands is called querying the database. Users can also modify the structure of the database itself (for example, adding a new column to a table) through the DBMS.

The Abstract View

A key feature of a database system is that it hides the low-level details of how data is physically stored and maintained on the storage device. It provides users with an abstract view of the data — they see tables, rows, and columns, not files, sectors, or pointers. A database system has a set of programs through which users or other application programs can access, modify, and retrieve the stored data. …