A behavioral notion of subtypingA Behavioral Notion of Subtyping BARBARAH. LISKOV MIT Laboratory for Computer Science and JEAN NETTE M. WING Carnegie Mellon University The use of hierarchy is unimportant component of object-oriented design. Hierarchy allows the use oft ype families, in which higher level supert ypes capt ure the behavior that all of their subt ypes havein common. Forthis methodology to beeffective, itisnecessary
