Exceptions in Object-oriented Languages

Object-oriented languages can be successfully used in the implementation of Information Systems, where persistent objects act as repositories of information, while class descriptions provide constraints on valid information states. We review here the need for occasionally permitting the existence of objects which violate the constraints stated in their class definitions, as well as the utility of allowing mutually contradictory class definitions, especially in class hierarchies. We then outline an approach which deals with the problems of persistent exceptional objects by exploiting a form of exception handling. The advantages gained by designing exception handling language features within an object-oriented paradigm are highlighted.