Claire Gardent

Talking about trees

In this paper we introduce a modal language LT for imposing constraints on trees, and an extension LT (LF) for imposing constraints on trees decorated with feature structures. The motivation for introducing these languages is to provide tools for formalising grammatical frameworks perspicuously, and the paper illustrates this by showing how the leading ideas of GPSG can be captured in LT (LF).In addition, the role of modal languages (and in particular, what we have called layered modal languages) as constraint formalisms for linguistic theorising is discussed in some detail.

XMG: eXtensible MetaGrammar

In this article, we introduce eXtensible MetaGrammar (XMG), a framework for specifying tree-based grammars such as Feature-Based Lexicalized Tree-Adjoining Grammars (FB-LTAG) and Interaction Grammars (IG). We argue that XMG displays three features that facilitate both grammar writing and a fast prototyping of tree-based grammars. Firstly, XMG is fully declarative. For instance, it permits a declarative treatment of diathesis that markedly departs from the procedural lexical rules often used to specify tree-based grammars. Secondly, the XMG language has a high notational expressivity in that it supports multiple linguistic dimensions, inheritance, and a sophisticated treatment of identifiers. Thirdly, XMG is extensible in that its computational architecture facilitates the extension to other linguistic formalisms. We explain how this architecture naturally supports the design of three linguistic formalisms, namely, FB-LTAG, IG, and Multi-Component Tree-Adjoining Grammar (MC-TAG). We further show how it permits a straightforward integration of additional mechanisms such as linguistic and formal principles. To further illustrate the declarativity, notational expressivity, and extensibility of XMG, we describe the methodology used to specify an FB-LTAG for French augmented with a unification-based compositional semantics. This illustrates both how XMG facilitates the modeling of the tree fragment hierarchies required to specify tree-based grammars and of a syntax/semantics interface between semantic representations and syntactic trees. Finally, we briefly report on several grammars for French, English, and German that were implemented using XMG and compare XMG with other existing grammar specification frameworks for tree-based grammars.

Higher-Order Coloured Unification and Natural Language Semantics

In this paper, we show that Higher-Order Coloured Unification - a form of unification developed for automated theorem proving - provides a general theory for modeling the interface between the interpretation process and other sources of linguistic, non semantic information. In particular, it provides the general theory for the Primary Occurrence Restriction which (Dalrymple et al., 1991)s analysis called for.

Tree Descriptions, Constraints and Incrementality

In (Duchier and Gardent, 1999), we presented a constraint-based approach for solving tree descriptions and described its application to the underspecified semantic representation of discourse advocated in (Gardent and Webber, 1998). As later work showed, the strength of the proposal is that it provides a general logical framework and a processing method which can be tailored depending on the application. For instance, (Duchier and Thater, 1999) shows that it can be customised to description-based syntactic parsing while (Egg et al., 1998) adapts it to deal with underspecified semantic representation at the sentential level. In this chapter, we indicate how the approach may be further extended to support incremental discourse processing.

Focus and Higher-Order Unification

Pulman has shown that Higher-Order Unification (HOU) can be used to model the interpretation of focus. In this paper, we extend the unification-based approach to cases which are often seen as a test-bed for focus theory: utterances with multiple focus operators and second occurrence expressions. We then show that the resulting analysis favourably compares with two prominent theories of focus (namely, Rooths Alternative Semantics and Krifkas Structured Meanings theory) in that it correctly generates interpretations which these alternative theories cannot yield. Finally, we discuss the formal properties of the approach and argue that even though HOU need not terminate, for the class of unification-problems dealt with in this paper, HOU avoids this shortcoming and is in fact computationally tractable.

A specification language for lexical functional grammars

This paper defines a language λ for specifying LFG grammars. This enables constraints on LFGs composite ontology (c-structures synchronised with f-structures) to be stated directly; no appeal to the LFG construction algorithm is needed. We use λ to specify schemata annotated rules and the LFG uniqueness, completeness and coherence principles. Broader issues raised by this work are noted and discussed.

Deaccenting and Higher-Order Unification

The HOU-based analysis of ellipsis was shown byDalrymple et al. (1991) and Shieber et al. (1996) to correctly capture thecomplex interaction of VP-ellipsis, scope and anaphora and claimed toextend to further related phenomena. When applied to deaccenting, theanalysis makes a strong prediction, namely that all anaphors occurringin the deaccented part of a deaccented utterance are parallelanaphors, i.e., anaphors that resolve to their parallel counterpart inthe source. I argue that this prediction is supported by the data andshow that it correctly captures the interaction of deaccenting withanaphora, (in)definiteness and focus.

A unification-based approach to multiple VP ellipsis resolution

An assumption shared by many theories of discourse is that discourse structure constrains anaphora resolution (cf. [Grosz and Sidner 1986] for definite NPs, [Lascarides and Asher 1991], [Nakhimovsky 1988] for temporal anaphora, [Webber 1990] for deictic pronouns and [Gardent 1991], [Prust and Scha 1990] for VP ellipsis). The aim of this paper is (i) to show that this assumption also applies to multiple VP ellipsis (VPE), (ii) to argue that other levels of linguistics information (such as syntax and semantics) interact with discourse structure in determining multiple VPE acceptability and (iii) to make these intuitions precise by providing a unification-based account of multiple VPE resolution.

Steuerung der Inferenz in der Diskursverarbeitung

SummarySemantic interpretation is an essential component of natural language understanding, which draws on extremely efficient language-based inference techniques. Such techniques are still lacking in computational systems for natural language processing. We have investigated specialized representation formalisms and suitable inference techniques that meet some of these desiderata. We have developed higher-order inference procedures to accurately represent linguistic ambiguities in terms of underspecification, and show how these procedures can be guided by information from other linguistic strata.ZusammenfassungSemantische Auswertung ist in der menschlichen Sprachverarbeitung unabdingbar und wird mittels sehr effizienter Inferenztechniken ausgeführt. In der maschinellen Sprachverarbeitung dagegen fehlen vergleichbare Verfahren. Wir haben spezialisierte Repräsentationsformalismen und auch geeignete Inferenzmethoden untersucht, die hier eine Verbesserung darstellen. Es wurden höherstufige Inferenzprozeduren zur paßgenauen Darstellung sprachlicher Mehrdeutigkeiten durch Unterspezifikation erarbeitet und Möglichkeiten aufgezeigt, diese durch Information aus anderen sprachlichen Ebenen zu steuern.

Back and Forth Through Time and Events

In this extended abstract back- and-forth structures are defined and applied to the semantics of natural language. Back- and-forth structures consist of an event structure and an interval structure communicating via a relational link; transitions in the one structure correspond to transitions in the other. Such structures enable us to view temporal constructions (such as tense, aspect, and temporal connectives) as methods of moving systematically between information sources. We illustrate this with a treatment of the English present perfect, and progressive aspect, that draws on ideas developed in Moens and Steedman (1988).