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<Paper uid="W98-1422">
  <Title>Fully Lexicalized Head-Driven Syntactic Generation</Title>
  <Section position="1" start_page="0" end_page="0" type="abstr">
    <SectionTitle>
Abstract
</SectionTitle>
    <Paragraph position="0"> We describe a new approach to syntactic generation with Head-Driven Phrase Structure Grammars (HPSG) that uses an extensive off-line preprocessing step. Direct generation algo* rithms apply the phra~se-structure rules (schemata) of the grammar on:line which is an computationally expensive step. Instead, we collect off-line for every lexical type of the HPSG grammar all minimally complete projections (called elementary trees) that can be derived with the schemata. This process is known as 'compiling HPSG to TAG' and derives a Lexicalized Tree-Adjoining Grammar (LTAG). The representation as an LTAG is 'fully lexicalized' in the sense that all grammatical information is directly encoded with the lexical item (as a set of elementary trees) and the combination operations are reduced from schema applications to the TAG primitives of adjunction and substitution. Given this LTAG, the generation task has a very different search space that Can be traversed very efficiently, avoiding the costly on-line applications of HPSG unification. The entire generation task from a semantic representation to a surface string is split into two tasks, a microplanner and a syntactic realizer. This paper discusses the syntactic generator and the preprocessing steps as implemented in the Verbmobil system.</Paragraph>
    <Paragraph position="1"> 1 Generation in a Speech-to-Speech System The syntactic generation algorithm and the preprocessing steps presented in this paper are integrated into the Verbmobil system (see \[Wahlster 1993, Bub; Wahlster, and Waibel 1997\]). It is a system for speech-~to-speech dialog translation. The input for the generation module VM-GECO 1 is generated by a semantic-based transfer component (see \[Dorna and Emele 1996\]). The interface language chosen comprises the encoding of target language-specific semantic information in a combination of Underspecified Discourse Representation Theory and Minimal Recursion Semantics (see \[Bos et al. 1996\] and \[Copestake, Flickinger, and Sag 1997\]).</Paragraph>
    <Paragraph position="2"> The internal architecture of the generation module is modularized: it is separated into two phases, a microplanner and a syntactic generator. Throughout the system, we emphasize declarativity, which is also a necessary precondition for a comprehensive off-line preprocessing of external knowledge bases-in particular the preprocessing of the underlying Head-Driven Phrase Structure Grammar (HPSG, see \[Pollard and Sag 1994\]) which has been developed at CSLI, reflecting the latest developments in the linguistic theory and with a fairly wide coverage and also covering phenomena of spoken language.</Paragraph>
    <Paragraph position="4"/>
  </Section>
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