Objects, Events, and Properties

Free-standing entities are in turn classified into OBJECTs and EVENTs. Figure 1 (repeated from Figure 2 in the body of the technical report (Mahesh, 1995)) shows the top-level hierarchy in the ontology. OBJECTs, EVENTs, and PROPERTYs constitute the concepts in the ontology which are represented as frames. The next level of classification is based on a division, albeit overlapping, of OBJECTs and EVENTs into the physical, social, and mental worlds. OBJECTs are further classified into PHYSICAL-OBJECTs, MENTAL-OBJECTs, and SOCIAL-OBJECTs. Similarly, EVENTs are classified into PHYSICAL-EVENTs, MENTAL-EVENTs, and SOCIAL-EVENTs. PROPERTYs are classified into RELATIONs and ATTRIBUTEs. This classification is based on whether they relate the concept they modify to another concept in the ontology, or, simply add a numerical or literal attribute to the concept. As such, the filler of a slot that is a RELATION must always be another concept and the filler of an attribute slot can never be a concept.