Slots and Facets

A slot is the basic mechanism for representing relationships between concepts. In fact, slot is the fundamental meta-ontological predicate based on which the entire ontology can be described axiomatically (see Appendix B). Most ``content'' slots are Properties which are themselves defined as concepts in the ontology. There is a closed class of special slots. These slots are described below.

All slots have all permissible facets except as mentioned for the special slots below. An additional constraint from the distinction between concepts and instances is that slots in concepts (other than the special slots listed below) have only Sem facets and slots in instances have only Value facets. Permissible facets are:

• Value: the filler of this facet is an actual value; it may be an instance of a concept, a literal symbol, a number, or another concept (in the case of the special slots listed below).
• Sem: the filler of a sem facet is either another concept or a literal, number, or scalar range. In any case, the filler serves as a selectional restriction on the filler of the slot. It is through these selectional restrictions that concepts in the ontology are related (or linked) to other concepts in the ontology (in addition to taxonomic links).
• Default: the filler of a default facet is the value of the slot in the absence of an explicit value facet. For the sake of simplicity, default facets are not inherited in the K ontology (and hence are not in much use either).
• Measuring-Unit: this facet is used to add a measuring unit for the number that fills the value or default facet of the same slot. Measuring units are also defined as concepts in the ontology.
• Salience: the salience facet can be used to indicate how important or central a slot is to the entire concept. This may be used in lexicons or actual TMRs to indicate the focus of a part of the text, but is not used in the ontology itself.
• Relaxable-to: this facet is used only in the lexicon and indicates to what extent a language permits a selectional constraint to be violated in nonliteral usage such as a metaphor or metonymy. The filler of this facet is a concept that indicates the maximal set of possible fillers beyond which the text should be considered anomalous.

In addition to slots and facets, additional structure is available through the notion of a View. Each facet can have multiple views. In the current representation, we use only one view called Common. All facets in all slots of concepts have the Common view. In fact, the view is transparent in the graphical ukarat tool.

• Special Slots