Representing Non Classical Concepts in Formal Ontologies: Prototypes and Exemplars

Concept representation is still an open problem in the field of ontology engineering and, more in general, of knowledge representation. In particular, it still remains unsolved the problem of representing "non classical" concepts, i.e. concepts that cannot be defined in terms of necessary and sufficient conditions. In this chapter we review empirical evidence from cognitive psychology, which suggests that concept representation is not an unitary phenomenon. In particular, it seems that human beings employ both prototype and exemplar based representations in order to represent non classical concepts. We suggest that a similar, hybrid prototype-exemplar based approach could be useful also in the field of formal ontology technology. 1. Representing Non Classical Concepts The representation of common sense concepts is still an open problem in ontology engineering and, more in general, in Knowledge Representation (KR) (see e.g. Frixione and Lieto in press). Cognitive Science showed the empirical inadequacy of the so-called “classical” theory of concepts, according to which concepts should be defined in terms of sets of necessary and sufficient conditions. Rather, Eleanor Rosch’s experiments (Rosch 1975) – historically preceded by the philosophical analyses by Ludwig Wittgenstein (Wittgestein 1953) – showed that ordinary concepts can be characterized in terms of prototypical information. These results influenced the early researches in knowledge representation: the KR practitioners initially tried to keep into account the suggestions coming from cognitive psychology, and designed artificial systems – such as frames (Minsky 1975) and early semantic networks (see e.g. Quillian 1968) – able to represent concepts in “non classical” (prototypical) terms (for early KR developments, see also the papers collected in Brachman and Levesque 1985). However, these early systems lacked clear formal semantics and a satisfactory metathoretic account, and were later sacrificed in favour of a class of formalisms