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<Paper uid="C90-3045">
  <Title>Synchronous Tree-Adjoining Grammars</Title>
  <Section position="2" start_page="0" end_page="0" type="intro">
    <SectionTitle>
1 Introduction
</SectionTitle>
    <Paragraph position="0"> Tree-adjoining grammars (TAG) constitute a grammatical formalism with attractive properties for the strong characterization of the syntax of natural langtmges, that is, characterization of the analysis trees of the expressions in the language (Kroch and Joshi, 1985; Kroch, 1989)) Among these properties are that o The domain of locality in TAGs is larger than lot formalisms lhat augment context-free grammars (such as lexical-functkmal, or generalized or head-driven phrase-structure grammar), and (r) The statements of dependencies and recursion possibilities in a tree are factored, the former following from primitive dependencies in elementary trees, the latter a consequence of an operatkm of adjunction of trees.</Paragraph>
    <Paragraph position="1"> These unique properties of TAGs present a challenge tot the application of TAGs beyond the limited confines of syntax, for instance, to the task of semantic interpretation or automatic tr~mslation of natural language. The slandm'd methods of moving beyond syntax to interpretation make use in one way or another of the compositional structure of the analysis tree that is manifested in the tree's derivation. Any version of compositional 1We assume familiarity throughout the paper with previous work on TAGs. See, for instance, the introduction by Joshi (1987). semantics, or syntax.directed translation relies on such a methodology to some extent. However, in the case of TAGs, the compositional structure of the tree is not miro rored by its derivational structure, so that a method for constructing semantics based on the compositional syntactic structure will be inherently nonderivational, that is, construction of the semantics will be independent of the derivation of the tree, and therefore subsequent.</Paragraph>
    <Paragraph position="2"> On the other hand, a method mirroring the derivational structure will not necessarily be compositional with respect to tile derived structures of expressions. AI+ tl~ough such a method would be quite different from ttle primarily compositional methods previously postulated, it may have advantages, given that certain aspects of language seem to be noncompositional. (See Section 4.) In this paper, we present a varim~t of TAGs, called synchronous TAGs, which characterize correstxmdences between languages. The formalism's intended usage is to relate expressions of natural languages to their associated semantics represented in a logical form language, or to their translations in another natural language; in summary, we intend the formalism to allow TAGs to be used beyond their role in syntax proper. We also discuss its application to concrete examples, and mention some computational issues that arise in its interpretation.</Paragraph>
  </Section>
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