ER Model, Notations of ER Model, ER Diagrams

1. E-R Diagrams:
• E-R model is a way to combine network and relational database ideas.
• In short ER model is a conceptual data model than views the real world as
entities and relationships.
• This diagram is mainly used to represent data objects in the pictorial or visual
form.
• The main advantage of the entity relationship model is that, when once it is
drawn it can be easily converted into relation or relational model. The
construction done in ER model can easily be transformed into relational tables.
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2. E-R Diagram Notations:
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3. Components of ER Diagram in DBMS:
• Rectangle – It represents entity in the ER Model.
• Ellipse – It represents attribute in the ER Model.
• Diamond – It represents relationship between entity and attribute.
• Line – It links attribute(s) to entity set(s) and entity set(s) to
relationship set(s).
• Doubles Ellipses – It represents multivalued attributes.
• Dashed Ellipses – It denotes derived attributes.
• Double lines – It indicates total participation of an entity in a
relationship set.
• Double Rectangle – It represents weak entity set.
• Double Diamonds – It represents weak relationships.
• Multiple ellipses connected to single ellipse using lines – It
represents single values attributes
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4. E-R Diagrams Examples:
E-R Diagram for customer branch and account relationship:
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5. E-R Diagrams Examples:
E-R Diagram for Medical Shop Management:
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6. E-R Diagrams Examples:
E-R Diagram for Library System:
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7. E-R Diagrams Examples:
E-R Diagram for Railway Reservation System:
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