Licensing and Tree Adjoining Grammar in Government Binding Parsing

LICENSING AND TREE ADJOINING GRAMMAR IN GOVERNMENT BINDING PARSING Robert Frank* Department of Computer and Information Sciences University of Pennsylvania Philadelphia, PA 19104 email: frank@ linc.cis.upenn.edu Abstract This paper presents an implemented, psychologically plau- sible parsing model for Government Binding theory gram- mars. I make use of two main ideas: (1) a generaliza- tion of the licensing relations of [Abney, 1986] allows for the direct encoding of certain principles of grammar (e.g. Theta Criterion, Case Filter) which drive structure build- ing; (2) the working space of the parser is constrained to the domain determined by a Tree Adjoining Grammar elementary tree. All dependencies and constraints are lo- caiized within this bounded structure. The resultant parser operates in linear time and allows for incremental semantic interpretation and determination of grammaticaiity. 1 Introduction This paper aims to provide a psychologically plausible mechanism for putting the knowledge which a speaker has of the syntax of a language, the competence gram- mar, to use. The representation of knowledge of language I assume is that specified by Government Binding (GB) Theory introduced in [Chomsky, 1981]. GB, as a com- petence theory, emphatically does not specify the nature of the language processing mechanism. In fact, "proofs" that transformational grammar is inadequate as a linguis- tic theory due to various performance measures are funda- mentally flawed since they suppose a particular connection between the grammar and parser [Berwick and Weinberg, 1984]. Nonetheless, it seems desirable to maintain a fairly direct connection between the linguistic competence and *I would like to thank the following for their valuable discussion and suggestions: Naoki Fukui, Jarnie Henderson, Aravind Joshi, Tony Kroch, Mitch Marcus, Michael Niv, Yves Schabes, Mark Steedman, Enric Vall- duv{. This work was pa~ially supported by ARO Grants DAAL03-89- C0031 PRI and DAAG29-84-K-0061 and DARPA grant N00014-85-K- 0018. The author is supported by a Unisys doctoral fellowship. its processing. Otherwise, claims of the psychological re- ality of this particular conception of competence become essentially vacuous since they cannot be falsified but for the data on which they are founded, i.e. grammaticality judgments. Thus, in building a model of language pro- cessing, I would like to posit as direct a link as is possible between linguistic competence and the operations of the parser while still maintaining certain desirable computa- tional properties. What are the computational properties necessary for psychological plausibility? Since human syntactic pro- cessing is an effortless process, we should expect that it take place efficiently, perhaps in linear time since sen- tences do not become more difficult to process simply as a function of their length. Determinism, as proposed by Marcus [1980], seems desirable as well. In addition, the mechanism should operate in an incremental fashion. Incrementality is evidenced in the human language pro- cessor in two ways. As we hear a sentence, we build up semantic representations without waiting until the sen- tence is complete. Thus, the semantic processor should have access to syntactic representations prior to an utter- ance's completion. Additionally, we are able to perceive …

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