Nonmonotonic inference rules for multiple inheritance with exceptions

The semantics of inheritance "hierarchies" with multiple inheritance and exceptions is discussed, and a partial semantics in terms of a number of structure types is defined. Previously proposed inference systems for inheritance with exceptions are discussed. A new and improved inference system is proposed, using a fixed number of nonmonotonic inference rules. The hierarchy is viewed as a set of atomic propositions using the two relations isa (subsumption) and nisa (nonsubsumption). General results concerning systems of nonmonotonic inference rules can immediately be applied to the proposed inference system.