Minimal Recursion Semantics as Dominance Constraints: Translation, Evaluation, and Analysis

Minimal Recursion Semantics as Dominance Constraints: Translation, Evaluation, and Analysis Ruth Fuchss,1 Alexander Koller,1 Joachim Niehren,2 and Stefan Thater1 1 Dept. of Computational Linguistics, Saarland University, Saarbrücken, Germany ∗ 2 INRIA Futurs, Lille, France {fuchss,koller,stth}@coli.uni-sb.de Abstract We show that a practical translation of MRS de- scriptions into normal dominance constraints is fea- sible. We start from a recent theoretical translation and verify its assumptions on the outputs of the En- glish Resource Grammar (ERG) on the Redwoods corpus. The main assumption of the translation— that all relevant underspecified descriptions are nets—is validated for a large majority of cases; all non-nets computed by the ERG seem to be system- atically incomplete. 1 Introduction Underspecification is the standard approach to deal- ing with scope ambiguity (Alshawi and Crouch, 1992; Pinkal, 1996). The readings of underspecified expressions are represented by compact and concise descriptions, instead of being enumerated explic- itly. Underspecified descriptions are easier to de- rive in syntax-semantics interfaces (Egg et al., 2001; Copestake et al., 2001), useful in applications such as machine translation (Copestake et al., 1995), and can be resolved by need. Two important underspecification formalisms in the recent literature are Minimal Recursion Seman- tics (MRS) (Copestake et al., 2004) and dominance constraints (Egg et al., 2001). MRS is the under- specification language which is used in large-scale HPSG grammars, such as the English Resource Grammar (ERG) (Copestake and Flickinger, 2000). The main advantage of dominance constraints is that they can be solved very efficiently (Althaus et al., 2003; Bodirsky et al., 2004). Niehren and Thater (2003) defined, in a theo- retical paper, a translation from MRS into normal dominance constraints. This translation clarified the precise relationship between these two related for- malisms, and made the powerful meta-theory of dominance constraints accessible to MRS. Their goal was to also make the large grammars for MRS ∗ Supported by the CHORUS project of the SFB 378 of the DFG. and the efficient constraint solvers for dominance constraints available to the other formalism. However, Niehren and Thater made three techni- cal assumptions: 1. that EP-conjunction can be resolved in a pre- processing step; 2. that the qeq relation in MRS is simply domi- nance; 3. and (most importantly) that all linguistically correct and relevant MRS expressions belong to a certain class of constraints called nets. This means that it is not obvious whether their result can be immediately applied to the output of practical grammars like the ERG. In this paper, we evaluate the truth of these as- sumptions on the MRS expressions which the ERG computes for the sentences in the Redwoods Tree- bank (Oepen et al., 2002). The main result of our evaluation is that 83% of the Redwoods sentences are indeed nets, and 17% aren’t. A closer analysis of the non-nets reveals that they seem to be sys- tematically incomplete, i. e. they predict more read- ings than the sentence actually has. This supports the claim that all linguistically correct MRS expres- sions are indeed nets. We also verify …

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