Building Parallel LTAG for French and Italian

Building Parallel LTAG for French and Italian Marie-H616ne Candito TALANA & UFRL, Universitd Paris 7, case 7003, 2, place Jussieu 75251 Paris Cedex 05 France marie-helene.candito@linguist.j ussieu.fr Abstract In this paper we view Lexicalized Tree Adjoining Grammars as the compilation of a more abstract and modular layer of linguistic description : the metagrammar (MG). MG provides a hierarchical representation of texico- syntactic descriptions and principles that capture the well-formedness of lexicalized structures, expressed using syntactic functions. This makes it possible for a tool to compile an instance of MG into an LTAG, automatically performing the relevant combinations of linguistic phenomena. We then describe the instantiation of an MG for Italian and French. The work for French was performed starting with an existing LTAG, which has been augmented as a result. The work for Italian was performed by systematic contrast with the French MG. The automatic compilation gives two parallel LTAG, compatible for multilingual NLP applications. 1. Introduction Lexicalized Tree Adjoining Grammars (LTAG) is a formalism integrating lexicon and grammar (Joshi, 87; Schabes et al, 88) : its description units arc lexicalized syntactic trees, the elementary trees. The formalism is associated with a tree-rewriting process that links sentences with syntactic structures (in either way), by combining the elementary trees with two operations, adjunction and substitution. We assume the following linguistic features for LTAG elementary trees (Kroch & Joshi, 85; • Abeill6, 91; Frank, 92): lexicalization : elementary trees arc anchored by at least one lexical item. • semantic coherence : the set of lexical items on the frontier of an elementary tree forms exactly one semantic unit I. • large domain of locality : the elementary trees anchored by a predicate contain positions for the arguments of the predicate. ' Thus semantically void lexical forms (functional words) do not anchor elementary trees on their own. And words composing an idiomatic expression are multiple anchors of the same elementary tree. This last feature is known as the predicate- argument cooccurrence principle (PACP). Trees anchored by a predicate represent the minimal structure so that positions for all arguments are included. These argumental positions are extended either by receiving substitution or by adjoining at a node. Adjunction is used to factor out reeursion. Figure 1 shows two elementary trees anchored by the French verbal form mange (eat-pres-sg), whose arguments in the active voice are a subject NP and a direct object NP 2. The first tree shows all arguments in canonical position. The second tree shows a relativized subject and a pronominal object (accusative clitic). The argumental nodes are numbered, according to their oblicity order, by an index starting at 0 in the unmarked case (active). So for instance in passive trees, the subject is number 1, not 0. 0 V~~O N NO* S N I,], ~ r I qui C115 V0 I mmlge Figure 1:2 elementary trees anchored by mange Though LTAG units used during derivation are lexicalized trees, the LTAG internal representation makes use of "pre-lexicalized" structures, that we will call tree …

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