UNIT I RELATIONAL DATABASES

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 1.1 Purpose of Database System

A database system is a combination of data, software, and rules that lets people store, manage, and retrieve information efficiently.

1. What makes up a database system?

  • Database – the organized collection of data (tables, records, fields)

  • DBMS (Database Management System) – software that manages the data
    Examples: MySQL, PostgreSQL, Oracle, MongoDB

  • Users & applications – people or programs that access the data

  • Hardware – servers, storage, and networks

  • Procedures – rules for using and maintaining the data

2. What does a DBMS do?

  • Stores large amounts of data safely

  • Allows fast searching and updating

  • Controls access (security)

  • Prevents data loss (backups & recovery)

  • Handles multiple users at the same time

3. Types of database systems

  • Relational databases – data stored in tables (most common)
    Example: MySQL, PostgreSQL

  • NoSQL databases – flexible structure (used for big data & web apps)
    Example: MongoDB, Firebase

  • Centralized databases – stored in one location

  • Distributed databases – data spread across multiple locations

4. Where are database systems used?

  • School systems (student records)

  • Social media apps

  • Online shopping websites

  • Banking systems

  • Games and mobile apps

5. Simple example

A school database might have:

  • Students table (ID, Name, Class)

  • Teachers table (ID, Subject)

  • Grades table (StudentID, Subject, Marks)

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