Entity Relationship Diagram

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Entity 

 Student is an Entity.


Attribute

A property or characteristic of an entity type.
Examples: FirstName, LastName, PhoneNo



If the attributes are composite, they are further divided in a tree like structure



Multivalued attributes are depicted by double ellipse. Example: PhoneNo

Derived attributes are depicted by dashed ellipse. Example: Age

Identifier
An attribute (or combination of attributes) that uniquely identify individual instances of an entity type
Roll_No is an identifier.(Primary Key)



Mapping to Relations
Student (Roll_No, Name, Class, Subject)

There can be composite identifiers.


Mapping to Relations
Flight (Flight_No, Date)



Mapping to Relations
Loan (loan-number, amount)
Payment (loan-number, payment-number, payment-date, payment-amount)

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