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<Paper uid="P01-1024">
  <Title>Topological Dependency Trees: A Constraint-Based Account of Linear Precedence</Title>
  <Section position="2" start_page="0" end_page="0" type="intro">
    <SectionTitle>
1 Introduction
</SectionTitle>
    <Paragraph position="0"> Linear precedence in so-called free word order languages remains challenging for modern grammar formalisms. To address this issue, we propose a new framework for dependency grammar which supports the modular decomposition of immediate dependency and linear precedence.</Paragraph>
    <Paragraph position="1"> Duchier (1999) formulated a constraint-based axiomatization of dependency parsing which characterized well-formed syntax trees but ignored issues of word order. In this article, we develop a complementary approach dedicated to the treatment of linear precedence.</Paragraph>
    <Paragraph position="2"> Our framework distinguishes two orthogonal, yet mutually constraining structures: a syntactic dependency tree (ID tree) and a topological dependency tree (LP tree). While edges of the ID tree are labeled by syntactic roles, those of the LP tree are labeled by topological fields (Bech, 1955). The shape of the LP tree is a flattening of the ID tree's obtained by allowing nodes to 'climb up' to land in an appropriate field at a host node where that field is available. Our theory of ID/LP trees is formulated in terms of (a) lexicalized constraints and (b) principles governing e.g. climbing conditions.</Paragraph>
    <Paragraph position="3"> In Section 2 we discuss the difficulties presented by discontinuous constructions in free word order languages, and briefly touch on the limitations of Reape's (1994) popular theory of 'word order domains'. In Section 3 we introduce the concept of topological dependency tree. In Section 4 we outline the formal framework for our theory of ID/LP trees. Finally, in Section 5 we illustrate our approach with an account of the word-order phenomena in the verbal complex of German verb final sentences.</Paragraph>
  </Section>
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