We describe one component of a "hybrid" Knowledge Representation Language (KRL) used for the development of Large Knowledge Bases (LKBs). This hybrid language involves two different aspects, the "descriptive" and the "definitional". The representation of the elementary events occurring in the real world (descriptive data = "Snoopy is Charlie Brown's beagle") is organized around "semantic predicates" (with "roles" and "arguments"); this gives rise to units called "predicative occurrences". The single predicative occurrences can be combined using logical, causal etc., relationships, giving rise to complex conceptual constructions ("binding occurrences"). "Abstract" conceptual units ("templates") which describe the expected properties of the "concrete" predicative and binding occurrences are placed in a specialization hierarchy (H_TEMP) characterized by the inheritance of properties and behaviours; the concrete "occurrences" constitute the "leaves" of this hierarchy. On the other hand, the "classes" representing the "general categories" of all the basic entities of the application domain which appear in the predicative occurrences are defined in terms of their own specialization hierarchy, H_CLASS (this is definitional data = "A beagle is a sort of hound / a hound is a dog ... "); the concrete "instances" of the defined classes are the "leaves" of this second hierarchy. The "definitional component" is not discussed in this article. The main difference between this KRL and other recent "hybrid" languages is that the "descriptive component" is not a first order predicate calculus language, but a highly structured semantic network. © 1992.
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