Semantic construction in F-TAG

Semantic construction in Feature-Based TAG Claire Gardent CNRS, Nancy BP 239 - Campus Scientifique 54506 Vandoeuvre-les-Nancy,France gardent@loria.fr Laura Kallmeyer TALaNa / Lattice, Universite Paris 7 2 place Jussieu 75251 Paris Cedex 05, France laura.kallmeyer@linguist.jussieu.fr Abstract We propose a semantic construction me- thod for Feature-Based Tree Adjoining Grammar which is based on the derived tree, compare it with related proposals and briefly discuss some implementation possibilities. 1 Introduction Semantic construction is the process of construc- ting semantic representations for natural language expressions. Perhaps the most well-known propo- sal for semantic construction is that presented in (Montague, 1974) in which grammar rules are ap- plied in tandem with semantic rules to construct not only a syntactic tree but also a lambda term representing the meaning of the described consti- tuent. Montague's approach gave rise to much further work aiming at determining the correct rules and representations needed to build a representation of natural language meaning. In particular, compu- tational grammars were developed which by and large took on Montague's proposal, building se- mantic representations in tandem with syntactic structures. Thus for instance, (Copestake et al., 2001) shows how to specify a Head Driven Phrase Struc- ture Grammar (HPSG) which supports the parallel construction of a phrase structure (or derived) tree and of a semantic representation, (Zeevat et al., 1987) shows it for Unification Categorial Gram- mar (UCG) and (Dalrymple, 1999) for Lexical Func- tional grammar (LFG). One grammatical framework for which the idea of a Montague style approach to semantic construc- tion has not been fully explored is Tree Adjoining Grammar (TAG, (Joshi and Schabes, 1997)). In that framework, the basic units are (elementary) trees and two operations are used to combine trees into bigger trees, namely, adjunction and substi- tution. Because the adjunction rule differs from standard phrase structure rules, two structures are associated with any given derivation: a derivation tree and a derived tree. While the derived tree is the standard phrase structure tree, the derivation tree records how the elementary trees used to build this derived tree are put together using adjunction and substitution. Furthermore, because TAG ele- mentary trees localise predicate-argument depen- dencies, the TAG derivation tree is usually taken to provide an appropriate basis for semantic construc- tion. And thus, the more traditional, "derived tree"- based approach is not usually pursued — An ex- ception to this is (Frank and van Genabith, 2001) which presents a fairly extensive specification of a derived tree based semantic construction for TAG and with which we will compare our approach in section 5. In this paper, we explore the idea of a semantic construction method which is based on the TAG derived tree and show how a Montague style (uni- fication based) approach to semantic construction can be applied to Feature-Based Tree Adjoining Grammar (FTAG, (Vijay-Shanker and Joshi, 1988)). We relate our approach to existing proposals and discuss two possibilities for implementation. 2 Hole semantics We start by introducing the semantic representa- tion language we use. As mentioned above, Mon- tague …

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