Information Structure in Topological Dependency Grammar

Information Structure in Topological Dependency Grammar Geert-Jan Kruijff Computational Linguistics Saarland University Saarbrticken, Germany gj@coli.uni - sb.de Denys Duchier INRIA Lorraine Nancy, France denys.duchier@loria.fr Abstract Topological Dependency Grammar (TDG) is a lexicalized dependency grammar formalism, able to model lan- guages with a relatively free word order. In such languages, word order variation often has an important function: the realization of information structure. The paper discusses how to integrate information structure into TDG, and presents a constraint-based approach to modelling information structure and the various means to realize it, focusing on (possibly simultaneous use of) word order and tune. 1 Introduction In this paper, we present an extension to Topolog- ical Dependency Grammar (Duchier and Debus- mann, 2001) enabling us to analyse e.g. word or- der variation and tune as means to indicate what is the topic and what is the focus of an expression — i.e. its information structure (cf. §2, §4). Us- ing a constraint-based approach, we can analyse the surface form of an expression in terms of the information structure that it realizes. The information structure of an expression is a core part of its meaning: it indicates how the ex- pression relates to the discourse context. Informa- tion structure thus constitutes a crucial factor in determining an expression's contextual appropri- ateness or interpretability. Particularly in applica- tions that involve human-computer interaction, in- formation structure has thus been found to have a great impact on the understandability of computer- generated language, e.g. question/answering dia- logues (Prevost and Steedman, 1994; Hoffman, 1995; Kruijff-Korbayova et al., 2003) or genera- tion (Kruijff-Korbayova et al., 2002). In this paper we concentrate on information structure and the syntax/semantics-interface: We want to be able to reconstruct an expression's in- formation structure at the level of meaning, given the expression's surface form. To realize information structure a language may employ a variety of means, not only word order or tune but also morphology or marked syntactic con- structions. Collectively we call these means struc- tural indications of informativity, after (Vallduvf and Engdahl, 1996; Kruijff, 2001). As §2 illustrates, languages are not restricted to using just a single means. Within a single expres- sion several types of indications can normally be used simultaneously. The indications may con- strain the expression's well-formedness, and it is through their interaction that the indications help realize information structure. It is precisely this interaction that presents a problem for existing accounts of information structure and its realization. Although accounts normally acknowledge that there are various types of structural indications, most of them focus solely on modelling the use of a single type of struc- tural indication. For example, (Steedman, 2000) focuses on tune, (Hoffman, 1995) or (Hajieova et al., 1995) focus on word order. Such focus would be unproblematic if it were clear how these accounts could be extended to cover multiple, interacting types of structural in- dications. However, even for (Steedman, 2000; Hoffman, 1995), which are the formally most de- tailed, this is by no means obvious. CCG's un- derlying …

Content truncated to 500 words