<?xml version="1.0" standalone="yes"?>
<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="3" start_page="0" end_page="0" type="intro">
    <SectionTitle>
1 Introduction
</SectionTitle>
    <Paragraph position="0"> This paper contrasts two frameworks for computational semantics, the proposal for semantics in LTAG described in (Kallmeyer and Romero, 2005) and LRS (Richter and Sailer, 2004), a computational semantics framework formulated in Head-Driven Phrase Structure Grammar (HPSG).</Paragraph>
    <Paragraph position="1"> There are significant differences between LTAG and HPSG. LTAG is a mildly context-sensitive lexicalized formalism characterized by an extended domain of locality. HPSG is based on the idea of a separation of the lexicon and syntactic structure and on the strict locality of general grammar principles that are formulated in an expressive and very flexible logical description language. These fundamental differences are reflected in the respective architectures for semantics: LTAG assumes a separate level of underspecified semantic representations; LRS uses the description logic of syntax for semantic specifications.</Paragraph>
    <Paragraph position="2"> However, despite the different mathematical structures, we find striking similarities between LTAG semantics with unification and LRS. They both show similar intuitions underlying specific analyses, use the same higher order type-theoretic language (Ty2, (Gallin, 1975)) as a means for specifying the truth conditions of sentences, and employ a feature logic in the combinatorial semantics instead of the lambda calculus. Because of these similarities, analyses using both approaches are closely related and can benefit from each other.</Paragraph>
    <Paragraph position="3"> The paper is structured as follows: Sections 2 and 3 will introduce the two frameworks. The next three sections (4-6) will sketch analyses of some phenomena in both frameworks that will reveal relevant relations between them. Section 7 presents a summary and conclusion.</Paragraph>
  </Section>
class="xml-element"></Paper>