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<Paper uid="P04-1032">
  <Title>Minimal Recursion Semantics as Dominance Constraints: Translation, Evaluation, and Analysis</Title>
  <Section position="2" start_page="2" end_page="2" type="intro">
    <SectionTitle>
1 Introduction
</SectionTitle>
    <Paragraph position="0"> Underspecification is the standard approach to dealing 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 explicitly. Underspecified descriptions are easier to derive 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.</Paragraph>
    <Paragraph position="1"> Two important underspecification formalisms in the recent literature are Minimal Recursion Semantics (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).</Paragraph>
    <Paragraph position="2"> The main advantage of dominance constraints is that they can be solved very efficiently (Althaus et al., 2003; Bodirsky et al., 2004).</Paragraph>
    <Paragraph position="3"> Niehren and Thater (2003) defined, in a theoretical paper, a translation from MRS into normal dominance constraints. This translation clarified the precise relationship between these two related formalisms, 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.</Paragraph>
    <Paragraph position="4"> and the efficient constraint solvers for dominance constraints available to the other formalism.</Paragraph>
    <Paragraph position="5"> However, Niehren and Thater made three techni- null cal assumptions: 1. that EP-conjunction can be resolved in a pre-processing step; 2. that the qeq relation in MRS is simply dominance; null 3. and (most importantly) that all linguistically correct and relevant MRS expressions belong  to a certain class of constraints called nets.</Paragraph>
    <Paragraph position="6"> This means that it is not obvious whether their result can be immediately applied to the output of practical grammars like the ERG.</Paragraph>
    <Paragraph position="7"> In this paper, we evaluate the truth of these assumptions 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 systematically incomplete, i. e. they predict more readings than the sentence actually has. This supports the claim that all linguistically correct MRS expressions are indeed nets. We also verify the other two assumptions, one empirically and one by proof.</Paragraph>
    <Paragraph position="8"> Our results are practically relevant because dominance constraint solvers are much faster and have more predictable runtimes when solving nets than the LKB solver for MRS (Copestake, 2002), as we also show here. In addition, nets might be useful as a debugging tool to identify potentially problematic semantic outputs when designing a grammar.</Paragraph>
    <Paragraph position="9"> Plan of the Paper. We first recall the definitions of MRS (SS2) and dominance constraints (SS3). We present the translation from MRS-nets to dominance constraints (SS4) and prove that it can be extended to MRS-nets with EP-conjunction (SS5). Finally we evaluate the net hypothesis and the qeq assumption on the Redwoods corpus, and compare runtimes (SS6).</Paragraph>
  </Section>
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