Data structures in databases at three levels: physical, logical, and conceptual.

1. Conceptual Level (High-Level / Global View)

Purpose: Shows what data is stored in the database, without worrying about how it’s stored.

• Focuses on entities, relationships, and constraints
• Independent of any DBMS or storage details

Example:

• Entities: Students, Courses
• Relationships: Students enroll in Courses
• Attributes: Student(id, name, age); Course(id, title)

Diagram: Entity-Relationship Diagram (ERD) is often used.

Key Point: Conceptual = “what the data is”, not how it’s stored.

2. Logical Level (Schema / Structure)

Purpose: Shows how data is organized logically inside a DBMS, without caring about physical storage.

• Focuses on tables, columns, data types, constraints
• Defines relations, primary keys, foreign keys
• DBMS independent in terms of storage, but specifies structure

Example (Relational Schema):