What is E-R Model ?

E-R ( Entity Relationship ) model

  • An E-R model was proposed by Peter Chen in 1971.
  • An Entity–relationship model  describes the structure of a database .
  • An ER model is a design or blueprint of a database .
  • An E-R model is a high-level data model. it is used to define the data elements and relationship for a specified system.
  • An ER model defines the conceptual view of a database.

 ER Diagram

Suppose we design a college database. In this database, the student and college will be an entity with attributes like address, name, id, age, clg_id , clg_name etc.

Geometric shapes and their meaning in an E-R Diagram :- 

Rectangle: Represents Entity sets.
Ellipses: Attributes
Diamonds: Relationship Set
Lines: They link attributes to Entity Sets and Entity sets to Relationship Set
Double Ellipses: Multi-valued Attributes
Dashed Ellipses: Derived Attributes
Double Rectangles: Weak Entity Sets

Components of a ER Diagram

there are three basic concepts

  1. Entities
  2. Attribute
  3. Relationship

Entities : A real-world thing either living or non-living that is easily recognizable and nonrecognizable. An entity may be any object, class, person or place. entity can be represented as rectangles.

Attribute : The attribute is used to describe the property of an entity. Eclipse is used to represent an attribute.

For example, id, age,  name, address, clg_id, clg_name etc. can be attributes of a student and college.

Relationship:  A relationship is used to describe the relation between entities. Diamond  is used to represent the relationship.

Types of relationship : there are many types of relationship .

  1. one – to – one relationship
  2. one – to – many relationship
  3. many – to – one relationship
  4. many – to – many relationship