• ER stands for Entity-Relationship model. It is a high level data model.
• If any data elements or relationship of any specified system can defined using this model.
• Conceptual design for database is developed in this model.
• Design view of data is very simple and easy to develop.
• Structure of the database is shown as a diagram called the Entity-Relationship diagram.

Component of ER Diagram:

Entity

• In an ER Diagram, Entity is represented as rectangles.
• An entity may be any object, class, person or place.

Attribute

• In an ER diagram attributes are represented using eclipse.
• Attribute describes the property of an entity.

Relationship

• Relationship are represented in an er diagram by diamond or rhombus.
• It is used to represent the relationship between entities.

Types of Relationship

One to one relationship

• When only one instance of an entity is associated with an relationship is known as one to one relationship.

One to many Relationship

• When only one instance of entity in the left is associated with more than one instance on the right is called one to many relationship.

Many-to-one relationship

• When more than one instance of entity in the left is associated with only one instance on the right associates with the relationship is called many to one relationship.

Many-to-many relationship

• When more than one instance of entity in the left is associated with more than one instance on the right associates with the relationship is called many to many relationship