Entity Relationship model (ER model)

  • The entity-relationship (E-R) data model is based on a perception of a real world that consists of a collection of basic objects, called entities, and of relationships among these objects.
  • An entity is a “thing” or “object” in the real world that is distinguishable from other objects. For example, each person is an entity, and bank accounts can be considered as entities.
  • A relationship is an association among several entities. For example, a depositor relationship associates a customer with each account that she has.
  • The set of all entities of the same type and the set of all relationships of the same type are termed an entity set and relationship set, respectively.
  • The overall logical structure (schema) of a database can be expressed graphically by an E-R diagram.

Component of E-R model

The E-R model consist of the following major components:

  • Entity
  • Attribute
  • Relationships
  • Key Attributes


  • An entity is a class of persons, places, object, events or concepts about which we need to collect and store data.
  • Each entity is distinguishable from the other entities.
  • categories of different entities include:
    • Persons
    • Places
    • Object
    • Events
    • Concepts


  • An attribute is a descriptive property or characteristic of an entity.
  • Same attribute can be logically grouped into super attributes called compound attribute.

Key Attributes

  • Key attribute is an attribute that uniquely identifies an entity in the entity set.