this paper, we have proposed novel methods for robust parsing that integrate the flexibility of linguistically motivated lexical descriptions with the robustness of statistical techniques. Our thesis is that the computation of linguistic structure can be localized if lexical items are associated with rich descriptions (Supertags) that impose complex constraints in a local context. The supertags are designed such that only those elements on which the lexical item imposes constraints appear within a given supertag. Further, each lexical item is associated with as many supertags as the number of different syntactic contexts in which the lexical item can appear. This makes the number of different descriptions for each lexical item much larger, than when the descriptions are less complex; thus increasing the local ambiguity for a parser. But this local ambiguity can be resolved by using statistical distributions of supertag co-occurrences collected from a corpus of parses. We have explored these ideas in the context of Lexicalized Tree-Adjoining Grammar (LTAG) framework. The supertags in LTAG combine both phrase structure information and dependency information in a single representation. Supertag disambiguation results in a representation that is effectively a parse (almost parse), and the parser needs `only' combine the individual supertags. This method of parsing can also be used to parse sentence fragments such as in spoken utterances where the disambiguated supertag sequence may not combine into a single structure. 1 Introduction In this paper, we present a robust parsing approach called supertagging that integrates the flexibility of linguistically motivated lexical descriptions with the robustness of statistical techniques. The idea underlying the approach is that the ...

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this paper, we study the problem of lexicalizing context-free grammars and show that it enables faster processing. In previous attempts to take advantage of lexicalization, a variety of lexicalization procedures have been developed that convert context-free grammars (CFGs) into equivalent lexicalized grammars. However, these procedures typically suffer from one or more of the following problems

This document describes a sizable grammar of English written in the TAG formalism and implemented for use with the XTAG system. This report and the grammar described herein supersedes the TAG grammar described in [Abeill'e et al., 1990]. The English grammar described in this report is based on the TAG formalism developed in [Joshi et al., 1975], which has been extended to include lexicalization ([Schabes et al., 1988]), and unification-based feature structures ([Vijay-Shanker and Joshi, 1991]). The grammar discussed in this report extends the grammar presented in [Abeill'e et al., 1990] in at least two ways. First, this grammar has more detailed linguistic analyses, and second, the grammar presented in this paper is fully implemented. The range of syntactic phenomena that can be handled is large and includes auxiliaries (including inversion), copula, raising and small clause constructions, topicalization, relative clauses, infinitives, gerunds, passives, adjuncts, it-clefts, wh-clefts,...

Recent developments in connectionist architectures for symbolic computation have made it possible to investigate parsing in a connectionist network while still taking advantage of the large body of work on parsing in symbolic frameworks. The work discussed here investigates syntactic parsing in the temporal synchrony variable binding model of symbolic computation in a connectionist network. This computational architecture solves the basic problem with previous connectionist architectures, while keeping their advantages. However, the architecture does have some limitations, which impose constraints on parsing in this architecture. Despite these constraints, the architecture is computationally adequate for syntactic parsing. In addition, the constraints make some significant linguistic predictions. These arguments are made using a specific parsing model. The extensive use of partial descriptions of phrase structure trees is crucial to the ability of this model to recover the syntactic st...

this paper). Assuming a structure as: (24) [Der Mann] 1 [sucht] 2 [t 1 den Hund t 2 ] where the subscripts on the traces correspond to structure sharing of the synsem values, the same analysis as for the subordinate clause (23) can be maintained: nominative is assigned to the trace and inherited by the preposed noun phrase, the positional restriction is only on the trace, whereas the positional restrictions on the preposed noun phrase result from the standard filler mechanism. 6.2 Argument Reduction

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This paper defines multiset-valued linear index gram- mar and unordered vector grammar with dominance links. The former models certain uses of multisetvalued feature structures in unification-based for- malisms, while the latter is motivated by word order variation and by "quasi-trees", a generalization of trees. The two formalisms are weakly equivalent, and an important subset is at most context-sensitive and polyno- mially parsable.

In this paper, we present a new technique called LightweightDependency Analysis which in conjunctionwith Supertag disambiguation provides a method for Robust Partial Parsing, called Almost Parsing. An overview is given of the XTAG system in which this technique is being developed. In addition, we propose alternate metrics for evaluation of partial parsers that can also serve to evaluate full parsers.

Abstract. A grammar model for concurrent, object-oriented natural language parsing is introduced. Complete lexical distribution of grammatical knowledge is achieved building upon the head-oriented notions of valency and dependency, while inheritance mechanisms are used to capture lexical generalizations. The underlying concurrent computation model relies upon the actor paradigm. We consider message passing protocols for establishing dependency relations and ambiguity handling. 1