3. DBMS Architecture – Three Levels

A Database Management System (DBMS) uses a three-level architecture to separate how data is stored, how it is structured, and how users see it. This makes the system flexible, secure, and user-friendly.

1️⃣ External Level (User View)

  • This is the highest level of abstraction.
  • It defines how individual users see the data.
  • Each user gets a customized view depending on their role.
  • Example: An accountant may only see salary details, while an HR manager sees employee records.

2️⃣ Conceptual Level (Logical View)

  • This is the middle level.
  • It describes the entire database structure logically.
  • Defines tables, relationships, and constraints.
  • It is common for all users and hides physical storage details.
  • Example: A schema showing tables like Students, Courses, and their relationships.

3️⃣ Internal Level (Physical Storage View)

  • This is the lowest level.
  • It explains how data is physically stored in memory or disk.
  • Includes storage methods, indexing, and access paths.
  • Example: Data stored as files, blocks, or records on disk.