tailieunhanh - Báo cáo khoa học: "SYNTACTIC AND SEMANTIC PARSABILITY"

This paper surveys some issues that arise in the study of the syntax and semantics of natural languages (NL's) and have potential relevance to the automatic recognition, parsing, and translation of NL's. An attempt is made to take into account the fact that parsing is scarcely ever thought about with reference to syntax alone; semantic ulterior motives always underly the assignment of a syntactic structure to a sentence. First I consider the state of the art with respect to arguments about the language-theoretic complexity of NL's: whether NL's are regular sets, deterministic CFL's, CFL's, or whatever. . | SYNTACTIC AND SEMANTIC PARSABILITY Geoffrey K. Pullum Syntax Research Center Cowell College UCSC Santa Cruz CA 95064 and Center for the Study of Language and Information Stanford CA 94305 ABSTRACT This paper surveys some issues that arise in the study of the syntax and semantics of natural languages NL s and have potential relevance to the automatic recognition parsing and translation of NL s. An attempt is made to take into account the fact that parsing is scarcely ever thought about with reference to syntax alone semantic ulterior motives always underly the assignment of a syntactic structure to a sentence. First I consider the state of the art with respect to arguments about the language-theoretic complexity of NL s whether NL s are regular sets deterministic CFL s CFL s or whatever. While English still appears to be a CFL as far as I can tell new arguments some not yet published appear to show for the first time that some languages are not CFL s. Next I consider the question of how semantic filtering affects the power of grammars. Then I turn to a brief consideration of some syntactic proposals that employ more or less modest extensions of the power of context-free grammars. 1. INTRODUCTION Parsing as standardly defined is a purely syntactic matter. Dictionaries describe parsing as analysing a sentence into its elements or exhibiting the parts of speech composing the sentence and their relation to each other in terms of government and agreement. But in practice as soon as parsing a natural language NL is under discussion people ask for much more than that. Let US distinguish three kinds of algorithm operating on strings of words recognition output a decision concerning whether the string is a member of the language or not parsing output a syntactic analysis of the string or an error message if the string is not in the language translation output a translation or set of translations of the string into some language of semantic representation or an error message