The Liskov substitution principle is one and considered only one definition of subtype, a kind of datatype. The name commonly used in the field of object-oriented computer programming for the definition of subtype introduced by Barbara Liskov and Jeannette Wing in a 1993 paper entitled Family Values: A Behavioral Notion of Subtyping. It was formulated in a subsequent paper as follows:
- Let q(x) be a property provable about objects x of type T. Then q(y) should be true for objects y of type S where S is a subtype of T.
Citeseer page for the original paper: http://citeseer.nj.nec.com/liskov94family.htmlExternal Links