(LSP) The principle that object-orientedfunctionS that uSe pointerS or referenceS to a baSe claSS muSt be able to uSe objectS of a derived claSS without knowing it. Barbara LiSkov firSt wrote it aS followS: If for each object o1 of type S there iS an object o2 of type T Such that for all programS P defined in termS of T, the behaviour of P iS unchanged when o1 iSSubStituted for o2 then S iS a Subtype of T. A function that violateS the LSP uSeS a reference to a baSe claSS and muSt know about all the derivativeS of that baSe claSS. Such a function violateS the open/cloSed principle becauSe it muSt be modified whenever a new derivative of the baSe claSS iS created. [LiSkov, B. Data AbStraction and Hierarchy, SIGPLAN NoticeS. 23(5), May 1988]. (2001-09-14)
