Automatic vocabulary expansion through narrative context
Karen Ehrlich · 1995
We present a partial computational theory of a cognitive agent's ability to acquire word meanings from natural-language contexts. The theory is implemented in SNePS, a knowledge-representation and reasoning system with facilities for parsing and generating fragments of English and for belief revision. We take a word's meaning, as understood by an agent, to be its relation to the rest of that agent's knowledge. However, because such knowledge is idiosyncratic and contains information not relevant to a conventional definition, we research means by which an agent can abstract such definitions from individual experience. We are not concerned with a prescriptively correct definition of a word so much as with understanding it as it is used. We investigate which aspects of meaning are typically salient to defining common nouns and verbs, and how definitions are revised in successive encounters with a word. Previously unknown aspects of meaning may be added, and less salient information deleted as more salient information is acquired. Such deletion does not, however, imply deletion from the agent's beliefs. There are, however, occasions when an agent's understanding may be erroneous or incomplete in a way that requires revision of a prior belief. If a word is used in a way that contradicts a previous meaning postulate, that postulate must be revised to render the agent's understanding of the narrative consistent with its other knowledge. We present computational methods for performing such revision. We present several demonstrations of our system learning word meanings through successive encounters while reading stories from Malory's Le morte D'Arthur. These demonstrations are compared with protocols taken from two human readers who reasoned aloud while reading the same passages and attempted to define the target words from context. We also discuss the limitations of our current system and present ideas for its further development. Potential applications of this work include education, computational lexicography, and cognitive science studies of narrative understanding.