An NRDR KB evolves into a hierarchy of concepts where each concept is defined as a collection of hierarchical rules with exceptions. To modify a concept definition, exception rules are added by a domain expert, they are never deleted or modified. This eases maintenance and development of a concept definition, but may cause inconsistencies to occur in the KB. We analyse the relation between cases and rules as the knowledge base evolves and as these inconsistencies occur. We explore what specific features an OO database model should accommodate to be used to implement an NRDR KB. The aim is that this in turn allows the use of the built-in mechanisms to manage the consistency of an evolving NRDR conceptual hierarchy. The significance of this paper is two folds: first, it describes an efficient mechanism maintaining consistency of an evolving classification hierarchy, using built-in schema evolution features of an OODBMS. Second, it proposes an intelligent interface for an OODBMS, to allow intelligent classification queries over stored objects.