Coordination in Tree Adjoining Grammars: Formalization and Implementation

In this paper we show that an account for coordination can be constructed using the derivation structures in a lexicalized Tree Adjoining Grammar (LTAG). We present a notion of derivation in LTAGs that preserves the notion of fixed constituency in the LTAG lexicon while providing the flexibility needed for coordination phenomena. We also discuss the construction of a practical parser for LTAGs that can handle coordination including cases of non-constituent coordination.Comment: 6 pages, 16 Postscript figures, uses colap.sty. To appear in the proceedings of COLING 199

Some Novel Applications of Explanation-Based Learning to Parsing Lexicalized Tree-Adjoining Grammars

In this paper we present some novel applications of Explanation-Based Learning (EBL) technique to parsing Lexicalized Tree-Adjoining grammars. The novel aspects are (a) immediate generalization of parses in the training set, (b) generalization over recursive structures and (c) representation of generalized parses as Finite State Transducers. A highly impoverished parser called a ``stapler'' has also been introduced. We present experimental results using EBL for different corpora and architectures to show the effectiveness of our approach.Comment: uuencoded postscript fil

Factoring Predicate Argument and Scope Semantics : underspecified Semantics with LTAG

In this paper we propose a compositional semantics for lexicalized tree-adjoining grammar (LTAG). Tree-local multicomponent derivations allow separation of the semantic contribution of a lexical item into one component contributing to the predicate argument structure and a second component contributing to scope semantics. Based on this idea a syntax-semantics interface is presented where the compositional semantics depends only on the derivation structure. It is shown that the derivation structure (and indirectly the locality of derivations) allows an appropriate amount of underspecification. This is illustrated by investigating underspecified representations for quantifier scope ambiguities and related phenomena such as adjunct scope and island constraints

Disambiguation of Super Parts of Speech (or Supertags): Almost Parsing

In a lexicalized grammar formalism such as Lexicalized Tree-Adjoining Grammar (LTAG), each lexical item is associated with at least one elementary structure (supertag) that localizes syntactic and semantic dependencies. Thus a parser for a lexicalized grammar must search a large set of supertags to choose the right ones to combine for the parse of the sentence. We present techniques for disambiguating supertags using local information such as lexical preference and local lexical dependencies. The similarity between LTAG and Dependency grammars is exploited in the dependency model of supertag disambiguation. The performance results for various models of supertag disambiguation such as unigram, trigram and dependency-based models are presented.Comment: ps file. 8 page

A Processing Model for Free Word Order Languages

Like many verb-final languages, Germn displays considerable word-order freedom: there is no syntactic constraint on the ordering of the nominal arguments of a verb, as long as the verb remains in final position. This effect is referred to as ``scrambling'', and is interpreted in transformational frameworks as leftward movement of the arguments. Furthermore, arguments from an embedded clause may move out of their clause; this effect is referred to as ``long-distance scrambling''. While scrambling has recently received considerable attention in the syntactic literature, the status of long-distance scrambling has only rarely been addressed. The reason for this is the problematic status of the data: not only is long-distance scrambling highly dependent on pragmatic context, it also is strongly subject to degradation due to processing constraints. As in the case of center-embedding, it is not immediately clear whether to assume that observed unacceptability of highly complex sentences is due to grammatical restrictions, or whether we should assume that the competence grammar does not place any restrictions on scrambling (and that, therefore, all such sentences are in fact grammatical), and the unacceptability of some (or most) of the grammatically possible word orders is due to processing limitations. In this paper, we will argue for the second view by presenting a processing model for German.Comment: 23 pages, uuencoded compressed ps file. In {\em Perspectives on Sentence Processing}, C. Clifton, Jr., L. Frazier and K. Rayner, editors. Lawrence Erlbaum Associates, 199

Anchoring a Lexicalized Tree-Adjoining Grammar for Discourse

We here explore a ``fully'' lexicalized Tree-Adjoining Grammar for discourse that takes the basic elements of a (monologic) discourse to be not simply clauses, but larger structures that are anchored on variously realized discourse cues. This link with intra-sentential grammar suggests an account for different patterns of discourse cues, while the different structures and operations suggest three separate sources for elements of discourse meaning: (1) a compositional semantics tied to the basic trees and operations; (2) a presuppositional semantics carried by cue phrases that freely adjoin to trees; and (3) general inference, that draws additional, defeasible conclusions that flesh out what is conveyed compositionally.Comment: 7 pages, uses aclcol.st

A note on the strong and weak generative powers of formal systems

AbstractThis paper is a note on some relationships between the strong and weak generative powers of formal systems, in particular, from the point of view of squeezing more strong power out of a formal system without increasing its weak generative power. We will comment on some old and new results from this perspective. Our main goal of this note is to comment on the strong generative power of context-free grammars, lexicalized tree-adjoining grammars (and some of their variants) and Lambek grammars, especially in the context of crossing dependencies, in view of the recent work of Tiede (Ph.D. Dissertation, Indiana University, Bloomington, 1999)

Phrase Structure and Intonational Phrases: Comments on the Papers by Marcus and Steedman

This paper is a commentary on two papers presented at the Workshop on Cognitive Models of Language, Sperlonga (Italy), May 1988. These two papers are: Description Theory and Intonation Boundaries by Mitch Marcus, and Syntax and Intonation Structure in Combinatory Grammar by Mark Steedman. Their approaches to the interface between syntax and metrical phonology are compared and certain problems with their approaches have been pointed out. A phrase structure-like approach, which is able to support some flexible phrasing and permit a set of analyses to hold simultaneously has been discussed also. This approach is based on structured objects as syntactic types rather than on curried functional syntactic types as in Steedman\u27s work