tailieunhanh - Báo cáo khoa học: "Topological Dependency Trees: A Constraint-Based Account of Linear Precedence"

We describe a new framework for dependency grammar, with a modular decomposition of immediate dependency and linear precedence. Our approach distinguishes two orthogonal yet mutually constraining structures: a syntactic dependency tree and a topological dependency tree. The syntax tree is nonprojective and even non-ordered, while the topological tree is projective and partially ordered. | Topological Dependency Trees A Constraint-Based Account of Linear Precedence Denys Duchier Programming Systems Lab Universitat des Saarlandes Geb. 45 Postfach 15 11 50 66041 Saarbriicken Germany duchier@ Ralph Debusmann Computational Linguistics Universitat des Saarlandes Geb. 17 Postfach 15 11 50 66041 Saarbrucken Germany rade@ Abstract We describe a new framework for dependency grammar with a modular decomposition of immediate dependency and linear precedence. Our approach distinguishes two orthogonal yet mutually constraining structures a syntactic dependency tree and a topological dependency tree. The syntax tree is non-projective and even non-ordered while the topological tree is projective and partially ordered. 1 Introduction 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. Duchier 1999 formulated a constraint-based ax-iomatization 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. 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 . climbing conditions. In Section 2 we discuss the difficulties presented by discontinuous constructions in free word order languages