An Efficient Context-Free Parser For Augmented Phrase-Structure Grammars

In this paper we present an efficient context-free (CF) bottom-up, non deterministic parser. It is an extension of the ICA (Immediate Constituent Analysis) parser proposed by Grishman (1976), and its major improvements are described. It has been designed to run Augmented Phrase-Structure Grammars (APSG) and performs semantic interpretation in parallel with syntactic analysis. It has been implemented in Franz Lisp and runs on VAX 11/780 and, recently, also on a SUN workstation, as the main component of a transportable Natural Language Interface (SAIL = Sistema per I'Analisi e I'lnterpretazione del Linguaggio). Subsets of grammars of italian written in different formalisms and for different applications have been experimented with SAIL. In particular, a toy application has been developed in which SAIL has been used as interface to build a knowledge base in MRS (Genesereth et al. 1980, Genesereth 1981) about ski paths in a ski environment, and to ask for advice about the best touristic path under specific weather and physical conditions.