(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 is suBstituted 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 principleBecause 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)
