Symmetry in Class and Type Hierarchy

Zhao, L. and Coplien, J.O.

The class concept is central in OO programming (OOP) to implement abstract data types and enforce encapsulation. Type hierarchy has been regarded as a useful technique for consistency during extension. Yet, the importance of class and type hierarchy extends beyond their technical merits. Specifically, a class classifies objects and a type hierarchy classifies classes. Classification is fundamental to design, and its place in program evolution and programming language structure can be elucidated through formal symmetry models. Symmetry is the interplay between an invariant and the possibility of change. This paper discusses the importance of classification in OOP and shows the connection between classification and symmetry in class and type hierarchies

Cite as: Zhao, L. and Coplien, J.O. (2002). Symmetry in Class and Type Hierarchy. In Proc. Fortieth International Conference on Technology of Object-Oriented Languages and Systems (TOOLS Pacific 2002), Sydney, Australia. CRPIT, 10. Noble, J. and Potter, J., Eds. ACS. 181-189.

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