The Representation of Defaults in Cyc

Abstract

This paper provides an account of the representation of defaults in Cyc and their semantics in terms of first order logic with reification. Default reasoning is a complex thing, and we have found it beneficial to separate various complex issues whose current best solution is likely to change now and then - such as deciding between extensions, preferring one default to another, etc. - and deal with them explicitly in the knowledge base, thus allowing us to adopt a simple (and hopefully fixed) logical mechanism to handle the basic nonmonotonicity itself. We also briefly describe how this default reasoning scheme is implemented in Cyc.