Providing Defaults in the Frames Portion of First-Order Logic Knowledge Bases

Reference: Fikes, R. Providing Defaults in the Frames Portion of First-Order Logic Knowledge Bases. Knowledge Systems Laboratory, June, 2000.

Abstract: A common feature of current representation systems is to provide a highly expressive representation language (e.g., first order logic) and to embed in that language a frame language or description logic that supports an object-oriented structuring of knowledge bases. The embedding of a frame language in a first order logic language suggests a tractable and principled means of incorporating defaults into first order logic. Namely, restrict statements regarding defaults and exceptions to defaults (i.e., abnormality with respect to specific defaults) to those that can be expressed in the frame language, and consider default statements to hold unless they are blocked by explicitly asserted exceptions or by exceptions that can be inferred from the inheritance axioms of the frame language. In this note, we present such a means of representing and reasoning with defaults. We describe the representation and reasoning scheme as an extension to the OKBC knowledge model, and use KIF to express the axioms that provide the semantics for the scheme. However, the scheme could be directly adapted to most any predicate calculus representation language that includes a monotonic frame language.

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