A flexible natural language parser based on a two-level representation of syntax

Abstract

In this paper we present a parser which al lows to make explicit the interconnections between syntax and semantics, to analyze the sentences in a quasi-deterministic fashion and, in many cases, to identify the roles of the various constituents even if the sentance is ill-formed. The main fea ture of the approach on which the parser is based consists in a two-level representation of the syn tactic knowledge: a first set of rules emits hy potheses about the constituents of the sentence and their functional role and another set of rules verifies whether a hypothesis satisfies the con straints about the well-formedness of sentences. However, the application of the second set of rules is delayed until the semantic knowledge con firms the acceptability of the hypothesis. If the semantics reject it, a new hypothesis is obtained by applying a simple and relatively unexpensive "natural" modification; a set of these modifica tions is predefined and only when none of them is applicable a real backup is performed: in most cases this situation corresponds to a case where people would normally garden path.