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<Paper uid="W06-1515">
  <Title>Sydney, July 2006. c(c)2006 Association for Computational Linguistics Constraint-based Computational Semantics: A Comparison between LTAG and LRS</Title>
  <Section position="8" start_page="113" end_page="113" type="concl">
    <SectionTitle>
7 Summary and Conclusion
</SectionTitle>
    <Paragraph position="0"> LTAG and LRS have several common characteristics: They both 1. use a Ty2 language for semantics; 2. allow underspecification (LTAG scope constraints [?] versus LRS component-of constraints a1); 3. use logical descriptions for semantic computation; 4. are designed for computational applications. Due to these similarities, some analyses can be modelled in almost identical ways (e.g., the quantifier scope analyses, and the identification of arguments using attribute values rather than functional application in the lambda calculus). We take the existence of this clear correspondence as indicative of deeper underlying insight into the functioning of semantic composition in natural languages. null Additionally, the differences between the frameworks that can be observed on the level of syntax carry over to semantics: 1. LTAG's extended domain of locality allows the localization within elementary trees of syntactic and semantic relations between elements far apart from each other on the level of constituent structure. 2. LTAG (both syntax and semantics) is a formalism with restricted expressive power that guarantees good formal properties. The restrictions, however, can be problematic. Some phenomena can be more easily described in a system such as HPSG and LRS while their description is less straightforward, perhaps more difficult or even impossible within LTAG. The concord phenomena described in section 7 are an example of this.</Paragraph>
    <Paragraph position="1"> A further noticable difference is that within the (Kallmeyer and Romero, 2005) framework, the derivation tree uniquely determines both syntactic and semantic composition in a context-free way. Therefore LTAG semantics is mildly context-sensitive and can be said to be compositional. As far as LRS is concerned, it is not yet known whether it is compositional or not; compositionality (if it holds at all) is at least less straightforward to show than in LTAG.</Paragraph>
    <Paragraph position="2"> In conclusion, we would like to say that the similarities between these two frameworks permit a detailed and direct comparison. Our comparative study has shed some light on the impact of the different characteristic properties of our frameworks on concrete semantic analyses.</Paragraph>
  </Section>
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