tailieunhanh - Báo cáo khoa học: "Formal aspects and parsing issues of dependency theory Vincenzo Lombardo and Leonardo Lesmo"

The paper investigates the problem of providing a formal device for the dependency approach to syntax, and to link it with a parsing model. After reviewing the basic tenets of the paradigm and the few existing mathematical results, we describe a dependency formalism which is able to deal with long-distance dependencies. Finally, we present an Earley-style parser for the formalism and discuss the (polynomial) complexity results. | Formal aspects and parsing issues of dependency theory Vincenzo Lombardo and Leonardo Lesmo Dipartimento di Informatica and Centro di Scienza Cognitiva Universita di Torino Svizzera 185 - 10149 Torino - Italy Vincenzo lesmo @ Abstract The paper investigates the problem of providing a formal device for the dependency approach to syntax and to link it with a parsing model. After reviewing the basic tenets of the paradigm and the few existing mathematical results we describe a dependency formalism which is able to deal with long-distance dependencies. Finally we present an Earley-style parser for the formalism and discuss the polynomial complexity results. 1. Introduction Many authors have developed dependency theories that cover cross-linguistically the most significant phenomena of natural language syntax the approaches range from generative formalisms Sgall et al. 1986 to lexically-based descriptions Mel cuk 1988 to hierarchical organizations of linguistic knowledge Hudson 1990 Fraser Hudson 1992 to constrained categorial grammars Milward 1994 . Also a number of parsers have been developed for some dependency frameworks Covington 1990 Kwon Yoon 1991 Sleator Temperley 1993 Hahn et al. 1994 Lombardo Lesmo 1996 including a stochastic treatment Eisner 1996 and an object-oriented parallel parsing method Neuhaus Hahn 1996 . However dependency theories have never been explicitly linked to formal models. Parsers and applications usually refer to grammars built around a core of dependency concepts but there is a great variety in the description of syntactic constraints from rules that are very similar to CFG productions Gaifman 1965 to individual binary relations on words or syntactic categories Covington 1990 Sleator Temperley 1993 . know SUBj X s SCOMP 1 likes SUBj oBJ John beans Figure 1. A dependency uee for the sentence I know John likes beans . The leftward or rightward orientation of the edges represents the order constraints the dependents that .

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