Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Parsing Minimalist Languages Henk Harkema - Univesité du Québec à Montréal In this paper I will present a formal specification of a recognizer for languages generated by Minimalist Grammars (Stabler, 1997). Minimalist Grammars are simple, formal grammars modeling some important aspects of the kind of grammars developed in the framework of Chomsky's Minimalist Program (Chomsky, 1995). A Minimalist Grammar is defined by a set of lexical items, which varies from language to language, and two universal structure building functions, which are defined on trees or configurations: merge and move. Michaelis (1998) has shown that the set of languages generated by Minimalist Grammars is mildly context-sensitive: it falls properly between the set of context-sensitive languages and the set of context-free languages. Mildly context-sensitive languages are assumed to be appropriately powerful for the description of natural languages (Joshi, 1985). Minimalist Grammars can move material from positions arbitrarily deep inside a sentence. This property contributes to the non-context-free nature of these grammars. Michaelis' equivalence result (Michaelis, 1998) permits a representation of Minimalist Grammars in which the operations of the grammar are characterized in such a way that they are strictly local. In this representation, configurations are reduced to those properties that determine their behavior with regard to the structure building functions merge and move. This representation will be used in this paper to derive a top-down recognizer for languages generated by Minimalist Grammars. The recognizer starts from the assumption that the sentence to be parsed is actually a grammatical sentence, and then tries to disassemble it into lexical items by repeatedly applying the structure building functions merge and move in reverse. The recognizer presented in this paper has the correct-prefix property: it goes through the input sentence from left to right and, in case of an ungrammatical sentence, it will halt at the first word that does not fit into a grammatical structure, i.e., the recognizer will not go beyond a prefix that cannot be extended to a grammatical sentence in the language. Similarly, the parser of the human sentence processor detects an ungrammaticality at the first word that makes a sentence ungrammatical, and for garden path sentences it will generally hesitate at the first word that does not fit into the structure that has been hypothesized for the sentence. This is a computationally advantageous property for a recognizer to have, because it prevents the recognizer from spending any effort on a sentence once it is known that it is ungrammatical. Besides contributing to a deeper understanding of Minimalist Grammars and theories that can be formalized in a similar fashion, e.g. Strict Asymmetry Grammars (e.g. Di Sciullo, 1999), the work reported in this paper may also be relevant for psycholinguistic inquiries. In most psycholinguistic proposals, the operations of the human parser are informally sketched in the context of a small set of example sentences, leaving open the question whether a parser with the desired properties covering the entire language actually exists. Another drawback of some psycholinguistic work is that it is based on simplistic and outdated conceptions of syntactic structure. Having a formal, sound and complete parsing model for Minimalist Grammars may help to remedy these problems. References: N. Chomsky, The Minimalist Program. MIT Press, 1995. A.M. Di Sciullo. The Local Asymmetry Connection. In: MIT Working Papers in Linguistics, vol. 35. MIT Dept. of Linguistics, 1999. A.K. Joshi. Tree Adjoining Grammars: How Much Context-Sensitivity is Required to Provide Reasonable Structural Descriptions? In: Natural Language Parsing: Psychological, Computational, and Theoretical Perspectives, D.R. Dowty, L. Karttunen, and A.M. Zwicky (eds.). Cambridge University Press, 1985. J. Michaelis. Derivational Minimalism is Mildly Context-Sensitive. In: Logical Aspects of Computational Linguistics, Lecture Notes in Artificial Intelligence, vol. 2014, M. Moortgat (ed.) Springer Verlag, 1998. E.P. Stabler. Derivational Minimalism. In: Logical Aspects of Computational Linguistics, Lecture Notes in Artificial Intelligence, vol. 1328, C. Rétoré (ed.). Springer Verlag, 1997.