Specifications and their use in defining subtypes
Barbara H. Liskov, Jeannette M. Wing · 1993
Specifications are useful because they allow reasoning about objects without concern for their implementations.Type hierarchies are useful because they allow types that share common properties to be designed as a family.This paper is concerned with the interaction between specifications and type hierarchies.We present a way of specifying types, and show how some extra information, in addition to specifications of the objects' methods, is needed to support reasoning.We also provide a new way of showing that one type is a subtype of another.Our technique makes use of information in the types' specifications and works even in a very general computational environment in which possibly concurrent users share mutable objects.