CLASSIFICATION-BASED REASONING

A representation formalism for N-ary relations, quantification and definition of concepts is described. Three types of conditions are associated with concepts: 1) necessary and sufficient properties, 2) contingent properties, and 3) necessary properties. It is also explained how complex chains of inferences can be accomplished by representing existentially quantified sentences, and concepts denoted by restrictive relative clauses as classification hierarchies. The representation structures that make possible the inferences are explained first, followed by the reasoning algorithms that draw the inferences from the knowledge structures. All the ideas explained in this paper have been implemented and are part of the information retrieval component of Snowy, a program that understands scientific paragraphs. An appendix containing a brief session with the program ends the paper.