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  • 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

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