ENTITY RELATIONSHIP MODEL
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In Software Design the way UML diagrams are going
to play the role, in Database design ER diagrams are
going to play the role for it.

ENTITY RELATIONSHIP MODEL is the conceptual
model by which we conceive structure of database,
mention relationships between different components
& identify the constraints that occur in the integrated
designing of a complete database system.
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An entity set may participate in a relation either
totally or partially.
DIAGRAMATIC NOTATION:
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Cardinality ratio limits the possible
combination entities that may participate in
corresponding relationship set
Mapping cardinality of a relationship are:
◦
◦
◦
◦
1 –1
1 – many
many – 1
Many-many
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One to One Relationship
1
1
MANAGER
DEPARTMENT
has
Many to One Relationship
M
EMPLOYEE
reports to
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1
MANAGER
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1..1
MANAGER
0..3
DEPARTMENT
manages
Each
department is
managed by
ONE manager
Each manager manages
UP TO 3 departments
(but need not manage
any department)
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Identify the Entities
Find the Relationships & Cardinalities
Identify the key attributes
Identify other relevant attributes
Draw the ER Diagram
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Supplier
Quotation
ITEM
RetailOutlet
Employee
Customer
Dependent
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