Representing reified relations in Loom

Abstract

This paper discusses the semantics and usage of reification as applied to relations and tuples. The reification of a tuple is a proposition object possessing a case role for each domain attribute in the tuple. The reification of a set of fillers of a role is an object sometimes referred to as a ‘roleset’. In the course of defining reification mechanisms for the Loom knowledge representation system, we have unearthed several open issues that come into focus when considering equivalence relations between these kinds of reified objects. Another type of reification produces an individual that represents a view of another individual filling a particular role. We present a number of semantic variations of this reification operation, and argue that the unbridled application of such reification operators has the potential to overwhelm the representation mechanism. We suggest that a regimen that merges various similar but non-equivalent classes of individuals might be preferable to a system that insists on unique representations for each possible abstraction of an individual.