"I Lied about the Trees" Or, Defaults and Definitions in Knowledge Representation

Abstract

Over the past few years, the notion of a “prototype ” (e.g., TYPICAL-ELEPHANT) seems to have caught on securely in knowledge representation research. Along with a way to specify default properties for instances of a description, proto-represen-tations allow the overriding, or “cancelling ” of properties that don’t apply in particular cases. This supposedly makes repre-senting exceptions (three-legged elephants and the like) easy; but, alas, it makes one crucial type of representation impossible-that of composite descriptions whose meanings are functions of the structure and interrelation of their parts. This article ex-plores this and other ramifications of the emphasis on default properties and “typical ” objects. Author’s Note: This short article has been circulating underground for