Inheritance

• Incremental Specification

• Possible increments:

  • add data or behavior
  • subtract data or behavior
  • redefine behavior

• Conceptual-modeling (ontological) view of inheritance:

  • inherit only in ISA hierarchies
  • ISA should mean “is a”

• Consequence: this restricts possible increments to:

  • only add data or behavior (no subtraction)
  • no redefinition that changes the meaning (can only optimize specifications, e.g., areas for polygons vs. for rectangles)

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