Entity Relationship Model

ER Model

• High-Level Data Model used to define the data elements and relatinship for a specified system.

• It consists of entity, attribute and relationship.

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Entity

• An entity can be an object, class, person or place.

• Represented By square.

• Types:

  • Strong Entity: They have key attribute.
  • Weak Entity: They dont have key attribute.

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Attribute

• Property of an entity.

• Represented by Eclipse.

• Types:

  • Key attribute

    • Represents a primary key.
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  • Composite Attribute

    • Attribute composed of other attribute.
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  • Multi-valued Attribute

    • Can have More than one value.
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  • Derived Attribute

    • Attribute derived from other attribute.
    • Represented by dashed ellipse.
    • Example: age

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Relationship

• One-to-one
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• One-to-many
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• Many-to-one
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• Many-to-many
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