describing all the parts of er daigram properly with diagrams

1. REPRESENTATION OF
ENTITY RELATIONSHIP
DIAGRAM
PRESENTED BY :
GITIKA
BCA 2(M)

2. ENTITY RELATIONSHIP DIAGRAM
DEFINATION:
ER DIAGRAM IS A VISUALL REPRESENTATION OF DATA THAT
DESCRIBES HOW THE DATA IS RELATED WITH EACH OTHER.
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3. SYMBOLS AND NOTATION IN ER DIGRAM
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4. ENTITY
Entities are represented by means of rectangles. Rectangles are named with the
entity set they represent.
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5. WEAK ENTITY
WEAK ENTITY IS AN ENTITY THAT DEPENDS ON ANOTHER ENTITY. WEAK ENTITY
DOESN’T HAVE KEY ATTRIBUTES OF THEIR OWN.DOUBLE RECTANGLE REPRESENTS
WEAK ENTITY.
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6. ATTRIBUTES
Attributes are properties of entities. Attributes are represented by means of
ellipses. Every eclipse represents one attribute and is directly connected to its
entity (rectangle).
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7. KEY ATTRIBUTE
KEY ATTRIBUTES REPRESENTS THE MAIN CHARACTERSTIC OF AN ENTITY.
IT IS USED TO REPRESENT PRIMARY KEY ELLIPSE WITH UNDERLYING LINES REPRESENT
KEY ATTRIBUTE.
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8. COMPOSITE ATTRIBUTES
If the attributes are composite, they are further divided in a tree like structure. Every node is
then connected to its attribute. That is composite attributes are represented by ellipse that
are connected with an ellipse.
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9. MULTIVALUED ATTRIBUTES
Multivalued attributes are depicted by double eclipse
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10. DERIVED ATTRIBUTES
Derived attributes are depicted by dashed eclipse.
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11. RELATIONSHIP
Relationships are represented by diamond shaped box. Name of the relationship is
written in the diamond-box. All entities (rectangles), participating in relationship,
are connected to it by a line.
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12. ONE TO ONE
When only one instance of entity is associated with the relationship, it is marked as '1'. This image
below reflects that only 1 instance of each entity should be associated with the relationship. It depicts
one-to-one relationship
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13. ONE TO MANY
 When more than one instance of entity is associated with the relationship, it is marked as 'N'. This image
below reflects that only 1 instance of entity on the left and more than one instance of entity on the right
can be associated with the relationship. It depicts one-to-many relationship.
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14. MANY TO ONE
 When more than one instance of entity is associated with the relationship, it is marked as 'N'. This image below
reflects that more than one instance of entity on the left and only one instance of entity on the right can be
associated with the relationship. It depicts many-to-one relationship.
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15. MANY TO MANY
 This image below reflects that more than one instance of entity on the left and more than one
instance of entity on the right can be associated with the relationship. It depicts many-to-many
relationship.
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16. EXAMPLE OF AN ER DIGRAM
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