Download Parsing Minimalist Languages Henk Harkema

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.