What is E-R diagram? Why use ER diagrams? What are the components of the ER diagram? Give an example of ER diagram.

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Question (AMIE, Winter 2019)
What is E-R diagram? Why use ER diagrams? What are the
components of the ER diagram? Give an example of ER
diagram.

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DEFINITION
The E.R diagram is a semantic data modelling tool that is
used to accomplish the goal of abstractly describing or
portraying data.
As the name implies, an ER diagram models data as
entities and relationships, and entities have
attributes.

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ENTITY
An entity is a thing about which we store data, for
example, a person, a bank account, a building.
So an entity can be a person, place, object, event, or
concept about which we wish to store data.

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RELATIONSHIP
A relationship is a link or association between entities.
Relationships are usually denoted by verb phrases.

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ATTRIBUTE
An attribute is a property or characteristic for an entity.
For example, an entity, AUTOMOBILE, may have attributes
type, color, vehicle_id, etc.

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EXAMPLE
In a University database, we might have entities for
Students, Courses, and Lecturers. Students entity can have
attributes like Rollno, Name, and DeptID. They might have
relationships with Courses and Lecturers.

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ER DIAGRAM

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EXAMPLE GRAPHIC

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