Packed rewriting for mapping semantics to kr

Abstract

This paper describes one component of a system being developed at PARC for deriving knowledge representation from free text. The component takes compositionally derived semantic representations and converts them to knowledge representations, intended for use by a back-end reasoning system. A resource sensitive rewriting system, originally developed for transfer in machine translation, is used for the conversion. This paper (i) discusses the system background and the need for an explicit mapping between semantic and knowledge representations, (ii) describes the rewriting system, with emphasis on its use of packing to manage ambiguity, and (iii) discusses the advantages of using such a system for semantics to KR mapping. Above and beyond a system component description, the prime goal of this paper is to show how the free-choice packing mechanisms developed for managing ambiguity in non-context free parsing [Maxwell and Kaplan, 1995] can profitably be extended beyond syntactic representations. 1 System Background Conversion of text to KR proceeds as follows. The XLE is used to parse text against a broad-coverage, hand-written English grammar [Riezler et. al, 2002]. The parse output is fed into a semantic interpreter, an implementation of the theory of “glue semantics ” [Dalrymple, 2003] that produces fully scoped, higher-order intensional logical forms of the kind familiar to traditional formal semanticists. These logical forms are then flattened to a clausal form, similar in some respects to clausal forms obtained by skolemizing and flattening first order formulas. These clauses are then passed through the compo-∗ This work builds on the efforts of numerous people. John Maxwell and Ron Kaplan for the library interface to XLE ambiguity management routines; Tracy King, Annie Zaenen, Anette Frank, Martin Forst, Stefan Riezler and Anubha Kothari for using and breaking the system while it was under development but coming back for more; Danny Bobrow, Cleo Condoravdi, Valeria Paiva, Reinhard Stolle, John Everett and Liz Coppock for work on KR; and Martin Kay for a prototype version of the rewrite system. Thanks also to the anonymous reviewers of this paper. This work was supported in part by the