Restricting the Weak-Generative Capacity of Synchronous Tree-Adjoining Grammars

The formalism of synchronous tree-adjoining grammars, a variant of standard tree-adjoining grammars (TAG), was intended to allow the use of TAGs for language transduction in addition to language specification. In previous work, the definition of the transduction relation defined by a synchronous TAG was given by appeal to an iterative rewriting process. The rewriting definition of derivation is problematic in that it greatly extends the expressivity of the formalism and makes the design of parsing algorithms difficult if not impossible. We introduce a simple, natural definition of synchronous tree-adjoining derivation, based on isomorphisms between standard tree-adjoining derivations, that avoids the expressivity and implementability problems of the original rewriting definition. The decrease in expressivity, which would otherwise make the method unusable, is offset by the incorporation of an alternative definition of standard tree-adjoining derivation, previously proposed for completely separate reasons, thereby making it practical to entertain using the natural definition of synchronous derivation. Nonetheless, some remaining problematic cases call for yet more flexibility in the definition; the isomorphism requirement may have to be relaxed. It remains for future research to tune the exact requirements on the allowable mappings.Comment: 21 pages, uses lingmacros.sty, psfig.sty, fullname.sty; minor typographical changes onl

Restricting the weak-generative capacity of synchronous tree-adjoining grammars

The formalism of synchronous tree-adjoining grammars, a variant of standard tree-adjoining grammars (TAG), was intended to allow the use of TAGs for language transduction in addition to language specification. In previous work, the definition of the transduction relation defined by a synchronous TAG was given by appeal to an iterative rewriting process. The rewriting definition of derivation is problematic in that it greatly extends the expressivity of the formalism and makes the design of parsing algorithms difficult if not impossible. We introduce a simple, natural definition of synchronous tree-adjoining derivation, based on isomorphisms between standard tree-adjoining derivations, that avoids the expressivity and implementability problems of the original rewriting definition. The decrease in expressivity, which would otherwise make the method unusable, is offset by the incorporation of an alternative definition of standard tree-adjoining derivation, previously proposed for completely separate reasons, thereby making it practical to entertain using the natural definition of synchronous derivation. Nonetheless, some remaining problematic cases call for yel more flexibility in the definition; the isomorphism requirement may have to be relaxed. It remains for future research to rune the exact requirements on the allowable mappings.Engineering and Applied Science

Separating Dependency from Constituency in a Tree Rewriting System

In this paper we present a new tree-rewriting formalism called Link-Sharing Tree Adjoining Grammar (LSTAG) which is a variant of synchronous TAGs. Using LSTAG we define an approach towards coordination where linguistic dependency is distinguished from the notion of constituency. Such an approach towards coordination that explicitly distinguishes dependencies from constituency gives a better formal understanding of its representation when compared to previous approaches that use tree-rewriting systems which conflate the two issues.Comment: 7 pages, 6 Postscript figures, uses fullname.st

Représenter et utiliser les contraintes de la langue orale à l'aide d'une grammaire lexicalisée d'arbres adjoints

Colloque avec actes et comité de lecture.Cet article souligne le problème de l'analyse grammaticale des énoncés oraux incomplets en contexte de dialogue homme-machine. Des contraintes minimales de l'oral sont cependant exploitables afin de rester prédictif face aux phénomènes d'ellipses. Nous proposons un enrichissement du formalisme LTAG afin de capter ces contraintes et d'adapter à l'oral une grammaire initialement conçue pour l'écrit

Synchronous grammars as tree transducers

Tree transducer formalisms were developed in the formal language theory community as generalizations of finite-state transducers from strings to trees. Independently, synchronous tree-substitution and -adjoining grammars arose in the computational linguistics community as a means to augment strictly syntactic formalisms to provide for parallel semantics. We present the first synthesis of these two independently developed approaches to specifying tree relations, unifying their respective literatures for the first time, by using the framework of bimorphisms as the generalizing formalism in which all can be embedded. The central result is that synchronous tree-substitution grammars are equivalent to bimorphisms where the component homomorphisms are linear and complete.Engineering and Applied Science

Sous-langage d'application et LTAG : le système EGAL

Colloque avec actes et comité de lecture.Nous présentons un système dédié à la conception et au test d'un sous-language d'application pour un système de Dialogue Homme-Machine. EGAL se base sur une grammaire LTAG générale de la langue qui est spécialisée à une application donnée à l'aide d'un corpus d'entraînement. Un double effort a porté premièrement sur la définition d'une méthodologie précise passant par une expérimentation de type Magicien d'Oz pour le recueil des corpus et des estimations de la représentativité du corpus de conception, et, deuxièmement, sur la spécification des composants du système en vue de mettre en oeuvre des outils convivaux, génériques et ouverts

D-STAG: a Formalism for Discourse Analysis based on SDRT and using Synchronous TAG

We propose D-STAG, a new formalism for the automatic analysis of discourse. The analyses computed by d-stag are hierarchical discourse structures annotated with discourse relations, which are compatible with discourse structures computed in sdrt. A discursive STAG grammar pairs up trees anchored by discourse connectives with trees anchored by (functors associated with) discourse relations.D-STAG est un nouveau formalisme pour l'analyse automatique de discours

An Alternative Conception of Tree-Adjoining Derivation

The precise formulation of derivation for tree-adjoining grammars has important ramifications for a wide variety of uses of the formalism, from syntactic analysis to semantic interpretation and statistical language modeling. We argue that the definition of tree-adjoining derivation must be reformulated in order to manifest the proper linguistic dependencies in derivations. The particular proposal is both precisely characterizable through a definition of TAG derivations as equivalence classes of ordered derivation trees, and computationally operational, by virtue of a compilation to linear indexed grammars together with an efficient algorithm for recognition and parsing according to the compiled grammar.Comment: 33 page

La sémantique dans les grammaires d'interaction

http://www.Lavoisier.frNous proposons d'intégrer la sémantique dans les grammaires d'interaction, formalisme qui a été conçu pour représenter la syntaxe des langues. Pour cela, nous ajoutons au formalisme un niveau supplémentaire qui s'appuie sur les mêmes principes fondamentaux que le niveau syntaxique : contrôle de la composition par un système de polarités et utilisation de la notion de description de structure pour exprimer la sous-spécification. À la différence du niveau syntaxique, les structures sont des graphes acycliques orientés et non des arbres localement ordonnés. L'interface entre les deux niveaux est assurée de façon souple par une fonction de liage qui associe à tout noeud syntaxique au plus un noeud sémantique

D-STAG : un formalisme d'analyse automatique de discours basé sur les TAG synchrones

International audienceNous proposons D-STAG, un nouveau formalisme pour l'analyse automatique de la structure discursive des textes. Les analyses produites par D-STAG sont des structures de discours hiérarchiques annotées de relations de discours, qui sont compatibles avec les structures de discours produites en SDRT. L'analyse discursive prolonge l'analyse phrastique, sans modifier celle-ci, ce qui rend envisageable la mise en oeuvre d'un analyseur de discours