DBMS BCA Unit-2 ER Model - Introduction Components of an E-R Model Entity Entity Identifier: Key Attributes Strong and Weak Entity Sets Attributes and Domain Types of Attributes Relationships E-R DIAGRAM ERD for STUDENT Entity ERD for CAR Entity Entity Types for a COMPANY Database Relationship Types of COMPANY Database THE RELATIONAL MODEL Structure of Relational Databases Super Keys and Candidate Keys Relational Constraints Database Operations and Constraint Violations


Entity

Entity
  • Entity is the fundamental item in any data model.
  • An entity is a ‘thing’ or ‘object’ in a real world that can be distinguished from all other objects.
    eg:- car, table, book, etc.
  • An entity need not be a physical entity, it can also represent a concept in real world.
    eg:- project, loan, etc.
  • It represents a class of things, not any one instance.
Entity Set or Entity Type
A collection of a similar kind of entities is called an Entity Set or Entity Type.