Conceptual Overlays: A Mechanism for the Interpretation of Sentence Meaning in Context

Abstract

This paper describes a context mechanism for a natural language understanding system. Since no sentence is ever perceived outside some context, it is reasonable to inquire into the nature of context as it affects the interpretation of sentence meaning at a deep conceptual level. A theory, called conce}tual over~. is described. This theory (1 defines C(Tl•···•Ti), the context established by the meaningful sequence of thoughts Tl···· ,Ti: (2) defines I(Ti+l• C(Tl, ... ,T;}), the high-level interpretation of Ti+l in the context established by Tl•··· ,Ti ; and (3) specifies an effective algorithm and data structure for computin~ I(T,K) for arbitrary thought Tin context K. In particular, a prototype LISP system, EX-SPECTRE-1, which solves simple cases of I(T2,C(T1)) is described. The system is based on an expectancy/fulfillment paradigm . Expectancies are spontaneously activated by a patterndirected invocation technique. Each expectancy implicitly references large chunks of commonsense algorithms. A collection of such-rmprfcit~tivated algorithms constitutes context, and the interpretive process is one of identifying future input as steps in these algorithms . Context switching and uses of I(T,K) in alanuage comprehension system are discussed.