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Introduction to Database Systems

Entity-Relationship Model

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ER Model

Entity-Relationship Model

ER Components

  • Entity: Real-world object (Student, Course)
  • Attribute: Property of entity (name, age)
  • Relationship: Association between entities (enrolls)

ER Diagram Notation

Relationship Cardinalities

Attribute Types

  • Simple: Atomic (age, name)
  • Composite: Divisible (address → street, city, zip)
  • Derived: Computed (age from DOB)
  • Multi-valued: Multiple values (phone numbers)
  • Key: Unique identifier (student_id)

ER to Relational Mapping