tailieunhanh - Báo cáo khoa học: "Regular tree grammars as a formalism for scope underspecification"

We propose the use of regular tree grammars (RTGs) as a formalism for the underspecified processing of scope ambiguities. By applying standard results on RTGs, we obtain a novel algorithm for eliminating equivalent readings and the first efficient algorithm for computing the best reading of a scope ambiguity. We also show how to derive RTGs from more traditional underspecified descriptions. | Regular tree grammars as a formalism for scope underspecification Alexander Koller University of Edinburgh Michaela Regneri regneri@ t University of Groningen Stefan Thater stth@ Saarland University Abstract We propose the use of regular tree grammars RTGs as a formalism for the underspecified processing of scope ambiguities. By applying standard results on RTGs we obtain a novel algorithm for eliminating equivalent readings and the first efficient algorithm for computing the best reading of a scope ambiguity. We also show how to derive RTGs from more traditional underspecified descriptions. 1 Introduction Underspecification Reyle 1993 Copestake et al. 2005 Bos 1996 Egg et al. 2001 has become the standard approach to dealing with scope ambiguity in large-scale hand-written grammars see . Copestake and Flickinger 2000 . The key idea behind underspecification is that the parser avoids computing all scope readings. Instead it computes a single compact underspecified description for each parse. One can then strengthen the underspecified description to efficiently eliminate subsets of readings that were not intended in the given context Koller and Niehren 2000 Koller and Thater 2006 so when the individual readings are eventually computed the number of remaining readings is much smaller and much closer to the actual perceived ambiguity of the sentence. In the past few years a standard model of scope underspecification has emerged A range of formalisms from Underspecified DRT Reyle 1993 to dominance graphs Althaus et al. 2003 have offered mechanisms to specify the semantic material of which the semantic representations are built up plus dominance or outscoping relations between these building blocks. This has been a very successful approach but recent algorithms for eliminating subsets of readings have pushed the expres sive power of these formalisms to their limits for instance Koller and Thater 2006 speculate that .