Generalization SemanticsFlavors of Inheritance

• Specification inheritance

  • yields type hierarchies
  • preconditions must not become stricter, postconditions not weaker
  • DQueue subtype-of Stack
  • contravariance
    • Stack::push: Stack x Element ? Stack
    • DQueue::push: Stack x Element ? Stack (possibly: DQueue)

• Specialization inheritance

  • yields is-a hierarchies
  • Integer is-a Rational
  • covariance
    • Rational::*: Rational x Rational ? Rational
    • Integer::*: Integer x Integer ? Integer

• Implementation inheritance

  • no conceptual relationship at all

not distinguished in UML!

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