Preemptive reification

Abstract

It is useful to express the location of a node in a semantic graph in terms of a sequence of knowledge-bearing arcs that lead to the node from a node that is used as a point of reference. If the arcs on which such "graph-based addressing expressions" depend disappear, the expressions become invalid. When an arcis reified as a node, the reified arcmay or may not be removed. If it is not removed, the semanticgraph may exhibit unnecessary complexity, ambiguity, and lack of parsimony. Alternatively, if the original arcis removed, the value of dependent graph-based addressing expressions may be lost. For systems intended to support collaborative knowledge aggregation, such as the Semantic Web, one way to resolve this dilemma is to disallow "lazy" reification, and, in effect, preemptively reify everything that may, at any future time, require reification. Preemptively reified nodes can be "virtual" until they are actually needed, thus effectively maintaining parsimony. The Reference Model of the Topic Maps paradigm, now under development in the ISO, shows how the need for "lazy" reification can be avoided by means of a fixed set of arctypes and rules used to represent fully elaborated assertions. © Springer-Verlag Berlin Heidelberg 2002.