A Critical Evaluation of Commensurable Abduction Models for Semantic Interpretation

Language interpretation involves mapping from a string of words to a representation of an interpretation of those words. The problem is to be able to combine evidence I'rom the lexicon, syntax, semantics, ,'rod pragmatics to arrive at the best of the many possible interpretations. Given the well-worn sentence "The box is in the pen," ~;yntax may say that "pen '~ is a noun, while lexical knowledge may say that "pen" most often means writing implement, less often means a fenced enclosure, and very rarely means a female swan. Semantics may say that the object of "in" is often an enclosure, and pragmatics may ::ay lhat the topic is hiding small boxes of illegal drugs im side aquatic birds, Thus there is evidence for.multiple intc.rpretations, and one needs some way to decide between them. In the past few years, some general approaches to interpretation have been advanced within an abduction framework. Charniak (1986) and Norvig (1987, 1989) m'e two examples. Abduction is a term coined by Pierce (1955) to describe the (unsound) inference rule that concludes A from the observation 13 and the role A ~ B, along with the fact that there is no "better" rule explaining B. In this paper we critically evaluate three recent alxluctire interpretation models, those of Chamiak and Goldman (1989); Hobbs, Stickel, Martin and Edwards (1988); a~(1 Ng and Mooney (1990). "Itmse three models add the important property of commensurability: all types of evidence are represented in a common currency that can be compared and combined. While commensurability is a desirable property, and there is a clear need for a way to compare alternate explanations, it appears that a single scalar measure is not enough to account for all types of processing. We present other problems for the abductive approach, and some tentative solutions.