LTAG semantics with semantic unification

This paper sets up a framework for LTAG (Lexicalized Tree Adjoining Grammar) semantics that brings together ideas from different recent approaches addressing some shortcomings of TAG semantics based on the derivation tree. Within this framework, several sample analyses are proposed, and it is shown that the framework allows to analyze data that have been claimed to be problematic for derivation tree based LTAG semantics approaches

Licensing german negative polarity items in LTAG

Our paper aims at capturing the distribution of negative polarity items (NPIs) within lexicalized Tree Adjoining Grammar (LTAG). The condition under which an NPI can occur in a sentence is for it to be in the scope of a negation with no quantifiers scopally intervening. We model this restriction within a recent framework for LTAG semantics based on semantic unification. The proposed analysis provides features that signal the presence of a negation in the semantics and that specify its scope. We extend our analysis to modelling the interaction of NPI licensing and neg raising constructions

Korean to English Translation Using Synchronous TAGs

It is often argued that accurate machine translation requires reference to contextual knowledge for the correct treatment of linguistic phenomena such as dropped arguments and accurate lexical selection. One of the historical arguments in favor of the interlingua approach has been that, since it revolves around a deep semantic representation, it is better able to handle the types of linguistic phenomena that are seen as requiring a knowledge-based approach. In this paper we present an alternative approach, exemplified by a prototype system for machine translation of English and Korean which is implemented in Synchronous TAGs. This approach is essentially transfer based, and uses semantic feature unification for accurate lexical selection of polysemous verbs. The same semantic features, when combined with a discourse model which stores previously mentioned entities, can also be used for the recovery of topicalized arguments. In this paper we concentrate on the translation of Korean to English.Comment: ps file. 8 page

Lexicalization and Grammar Development

In this paper we present a fully lexicalized grammar formalism as a particularly attractive framework for the specification of natural language grammars. We discuss in detail Feature-based, Lexicalized Tree Adjoining Grammars (FB-LTAGs), a representative of the class of lexicalized grammars. We illustrate the advantages of lexicalized grammars in various contexts of natural language processing, ranging from wide-coverage grammar development to parsing and machine translation. We also present a method for compact and efficient representation of lexicalized trees.Comment: ps file. English w/ German abstract. 10 page

Binding theory in LTAG

This paper provides a unification-based implementation of Binding Theory (BT) for the English language in the framework of feature-based lexicalized tree-adjoining grammar (LTAG). The grammar presented here does not actually coindex any noun phrases, it merely outputs a set of constraints on co- and contraindexation that may later be processed by a separate anaphora resolution module. It improves on previous work by implementing the full BT rather than just Condition A. The main technical innovation consists in allowing lists to appear as values of semantic features

Punctuation in Quoted Speech

Quoted speech is often set off by punctuation marks, in particular quotation marks. Thus, it might seem that the quotation marks would be extremely useful in identifying these structures in texts. Unfortunately, the situation is not quite so clear. In this work, I will argue that quotation marks are not adequate for either identifying or constraining the syntax of quoted speech. More useful information comes from the presence of a quoting verb, which is either a verb of saying or a punctual verb, and the presence of other punctuation marks, usually commas. Using a lexicalized grammar, we can license most quoting clauses as text adjuncts. A distinction will be made not between direct and indirect quoted speech, but rather between adjunct and non-adjunct quoting clauses.Comment: 11 pages, 11 ps figures, Proceedings of SIGPARSE 96 - Punctuation in Computational Linguistic

XMG : eXtensible MetaGrammar

International audienceIn this article, we introduce eXtensible MetaGrammar (xmg), a framework for specifying tree-based grammars such as Feature-Based Lexicalised Tree-Adjoining Grammars (FB-LTAG) and Interaction Grammars (IG). We argue that xmg displays three features which 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 modelling 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\ to other existing grammar specification frameworks for tree-based grammars

A Lexicalized Tree Adjoining Grammar for English

This paper presents a sizable grammar for English written in the Tree Adjoining grammar (TAG) formalism. The grammar uses a TAG that is both lexicalized (Schabes, Abeillé, Joshi 1988) and feature-based (Vijay-Shankar, Joshi 1988). In this paper, we describe a wide range of phenomena that it covers. A Lexicalized TAG (LTAG) is organized around a lexicon, which associates sets of elementary trees (instead of just simple categories) with the lexical items. A Lexicalized TAG consists of a finite set of trees associated with lexical items, and operations (adjunction and substitution) for composing the trees. A lexical item is called the anchor of its corresponding tree and directly determines both the tree\u27s structure and its syntactic features. In particular, the trees define the domain of locality over which constraints are specified and these constraints are local with respect to their anchor. In this paper, the basic tree structures of the English LTAG are described, along with some relevant features. The interaction between the morphological and the syntactic components of the lexicon is also explained. Next, the properties of the different tree structures are discussed. The use of S complements exclusively allows us to take full advantage of the treatment of unbounded dependencies originally presented in Joshi (1985) and Kroch and Joshi (1985). Structures for auxiliaries and raising-verbs which use adjunction trees are also discussed. We present a representation of prepositional complements that is based on extended elementary trees. This representation avoids the need for preposition incorporation in order to account for double wh-questions (preposition stranding and pied-piping) and the pseudo-passive. A treatment of light verb constructions is also given, similar to what Abeillé (1988c) has presented. Again, neither noun nor adjective incorporation is needed to handle double passives and to account for CNPC violations in these constructions. TAG\u27S extended domain of locality allows us to handle, within a single level of syntactic description, phenomena that in other frameworks require either dual analyses or reanalysis. In addition, following Abeillé and Schabes (1989), we describe how to deal with semantic non compositionality in verb-particle combinations, light verb constructions and idioms, without losing the internal syntactic composition of these structures. The last sections discuss current work on PRO, case, anaphora and negation, and outline future work on copula constructions and small clauses, optional arguments, adverb movement and the nature of syntactic rules in a lexicalized framework

Research in the Language, Information and Computation Laboratory of the University of Pennsylvania

This report takes its name from the Computational Linguistics Feedback Forum (CLiFF), an informal discussion group for students and faculty. However the scope of the research covered in this report is broader than the title might suggest; this is the yearly report of the LINC Lab, the Language, Information and Computation Laboratory of the University of Pennsylvania. It may at first be hard to see the threads that bind together the work presented here, work by faculty, graduate students and postdocs in the Computer Science and Linguistics Departments, and the Institute for Research in Cognitive Science. It includes prototypical Natural Language fields such as: Combinatorial Categorial Grammars, Tree Adjoining Grammars, syntactic parsing and the syntax-semantics interface; but it extends to statistical methods, plan inference, instruction understanding, intonation, causal reasoning, free word order languages, geometric reasoning, medical informatics, connectionism, and language acquisition. Naturally, this introduction cannot spell out all the connections between these abstracts; we invite you to explore them on your own. In fact, with this issue it’s easier than ever to do so: this document is accessible on the “information superhighway”. Just call up http://www.cis.upenn.edu/~cliff-group/94/cliffnotes.html In addition, you can find many of the papers referenced in the CLiFF Notes on the net. Most can be obtained by following links from the authors’ abstracts in the web version of this report. The abstracts describe the researchers’ many areas of investigation, explain their shared concerns, and present some interesting work in Cognitive Science. We hope its new online format makes the CLiFF Notes a more useful and interesting guide to Computational Linguistics activity at Penn