Coping With Dynamic Syntactic Strategies: An Experimental Environment for an Experimental Parser

COPING WITH DYNAMIC SYNTACTIC STRATEGIES: AN EXPERIMENTAL ENVIRONMENT FOR AN EXPERIMENTAL PARSER Oliviero Stock I.P. - Consiglio Nazionale delle Ricerche Via dei Monti Tiburtini 509 00157 Roma, Italy ABSTRACT An environment built around WEDNESDAY 2, a chart based parser is introduced. The environment is in particular oriented towards exploring dynamic aspects of parsing. It includses a number of specialized tools that consent an easy, graphics-based interaction with the parser. It is shown in particular how a combination of the characteristics of the parser (based on the lexicon and on dynamic unification) and of the environment allow a nonspecialized user to explore heuristics that may alter the basica control of the system. In this way, for instance, a psycholinguist may explore ideas on human parsing strategies, or a "language engineer" may find useful heuristics for parsing within a particular application. 1. Introduction Computer-based environments for the linguist are conceived as sophisticated workbenches, built on AI workstations around a specific parser, where the linguist can try out his/her ideas about a grammar for a certain natural language. In doing so, he/she can take advantage of rich and easy-to-use graphic interfaces that "know" about linguistics. Of course behind all this lies the idea that cooperation with linguists will provide better results in NLP. To substantiate this assumption it may be recalled that some of the most interesting recent ideas on syntax have been developed by means of joint contributions from linguists and computational linguists. Lexical-Functional Grammar [Bresnan & Kaplan 1982], GPSG [Gazdar 1981], Functional Grammar [Kay 1979], DCG [Pereira & Warren 1980], TAG [Joshi & Levy 1982] are some of these ideas. Instances of the tools introduced above are the LFG environment, which was probably the first of its kind, an environment built by Ron Kaplan for Lexical- Functional Grammars, DPATR, built by Lauri Karttunen and conceived as an environment that would suit linguists of a number of different schools all committed to a view of parsing as a" process that makes use of an unification algorithm. We have developed an environment with a somewhat different purpose. Besides a number of tools for entering data in graphic mode and inspecting resulting structures, it provides a means for experimenting with strategies in the course of the parsing process. We think that this can be a valuable tool for gaining insight in the cognitive aspects of language processing as well as for tailoring the behaviour of the processor when used with a particular (sub)language. In this way an attempt can be made to answer basic questions when following a nondeterministic approach: what heuristics to apply when facing a certain choice point, what to do when facing a failure point, i.e. which of the pending processes to activate, taking account of information resulting from the failure? Of course this kind of environment makes sense only because the parser it works on has some characteristics that make it a psychologically interesting realization. 2. Motivation of the parser We shall classify psychologically motivated parsers in three main categories. …

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