27. Generalization, Classification, Inheritance

• Finding Classes, continued:

  • Inheritance (generalization) is used to represent commonality among concepts.

  • Commonality must be actively sought.

  • Generalization and classification are high-level activities that yield lasting results.

  • Classification should be of aspects of our own model, not aspects valid in other areas.

• For example, in mathematics a circle is a kind of an ellipse, but in most programs a circle should not be derived from an ellipse or an ellipse derived from a circle. The often heard arguments because that's the way it is in mathematics is not conclusive and most often wrong.

• In most systems circle and ellipse will provide independent sets of operations that are not subsets of each other.