Default reasoning and inheritance mechanisms on type hierarchies

Type hierarchies abound in Artificial Intelligence, Data Bases and Programming Languages. Although their size, use and complexity differs, all share a central inference mechanism: Inheritance of information, their raison d'etre. This paper discusses various types of type hierarchies and inheritance mechanisms, concluding with a proposed generalized inheritance mapping approach to resolve issues of lateral and upward inheritance (to augment the traditional downward approach), as well as default reasoning and limited non-monotonic inference.