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Entity Set Corelations

Specialisation

  • A specialisation indicates that the child has all attributes of the parent, but also adds something more
  • This is referred to as attribute inheritance, and drawn with a triangular arrow
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Overlapping and Disjoint Specialisation

  • Overlapping children sets means that that a member of a parent class can belong in both child classes
  • Meanwhile in disjoint specialisation, a parent can only have one of its children's attributes
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Generalisation

A generalisation is the inverse of a specialisation. In it, a number of entity sets sharing some features are combined into a higher-level set. The terms specialisation and generalisation are interchangeable

Completeness Contstraint

The completeness constraint specifies whether or not a parent entity must overlap with one of its children * Total Generalisation - The parent must share all attributes with one of its children * Partial Generalisation - The parent need not have the exact same attributes as any of its children

A total generalisation is indicated with a broken line, and a total label on the diagram.

Aggreagation

In an aggregation, multiple entities and / or relationships are abstracted into one aggregate entity

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