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<Paper uid="E06-2005">
  <Title>XMG - An expressive formalism for describing tree-based grammars</Title>
  <Section position="2" start_page="0" end_page="0" type="intro">
    <SectionTitle>
1 Introduction
</SectionTitle>
    <Paragraph position="0"> It is well known that grammar engineering is a complex task and that factorizing grammar information is crucial for the rapid development, the maintenance and the debugging of large scale grammars. While much work has been deployed into producing such factorizing environments for standard unification grammars, less attention has been paid to the issue of developing such environmentsfor &amp;quot;treebased grammars&amp;quot;that is, grammars like Tree Adjoining Grammars (TAG) or Tree Description Grammars where the basic unit of information is a tree rather than a category encoded in a feature structure.</Paragraph>
    <Paragraph position="1"> For these grammars, two trends have emerged to automatize tree-based grammar production: systems based on lexical rules (see (Becker, 2000)) and systems based on combination of classes (also called metagrammar systems, see (Candito, 1999), (Gaiffe et al., 2002)).</Paragraph>
    <Paragraph position="2"> 1We are grateful to Claire Gardent for useful comments on this work. This work is partially supported by an INRIA grant.</Paragraph>
    <Paragraph position="3"> Inthis paper, wepresent ametagrammar system for tree-based grammars which differs from comparable existing approaches bothlinguistically and computationally.</Paragraph>
    <Paragraph position="4"> Linguistically, the formalism we introduce is both expressive and extensible. In particularly, we show that it supports the description and factorization both of trees and of tree descriptions; that it allows the synchronized description of several linguistic dimensions (e.g., syntax and semantics) and that it includes a sophisticated treatment of the interaction between inheritance and identifier naming.</Paragraph>
    <Paragraph position="5"> Computationally, the production of a grammar from a metagrammar is handled using powerful and well-understood logic programming techniques. A metagrammar is viewed as an extended definite clause grammar and compiled using a virtual machine closely resembling the Warren's Abstract Machine. Thegeneration ofthetreessatisfying a given tree description is furthermore handled using a tree description solver.</Paragraph>
    <Paragraph position="6"> The paper is structured as follows. We begin (section 2) by introducing the linguistic formalism used for describing and factorizing tree based grammars. We then sketch the logic programming techniques used by the metagrammar compiler (section 3). Section 4 presents some evaluation results concerning the use of the system for implementing different types of tree based grammars. Section 5 concludes with pointers for further research and improvements.</Paragraph>
  </Section>
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