Weighted Interaction of Syntax and Semantics in Natural Language Analysis

The present paper discusses the extensions to the parsing strategies adopted for FIDO (a Flexible Interface for Database Operations). The parser is able to deal with ill-formed inputs (syntactically ill - formed sentences, fragments, conjunctions, etc.) because of the strict cooperation among syntax and semantics. The syntactic knowledge is represented by means of packets of condition-action rules associated with syntactic categories. The non-determinism is mainly handled by means of rules which restructure the parse tree (called "natural changes") so that the use of backtracking is strongly limited. In order to deal with difficult cases in which no clear-cut mechanism exists for excluding an interpretation, a weighting mechanism has been added to the parser so that it is possible to explore few different hypotheses in parallel and to choose the best one on the basis of complex interaction among syntax and semantics.