Syntactic/Semantic Coupling in the BBN DELPHI System

We have recently made significant changes to the BBN DELPHI syntactic and semantic analysis component. These goal of these changes was to maintain the fight coupling between syntax and semantics characteristic of earlier versions of DELPHI, while making it possible for the system to provide useful semantic interpretations of input for which complete syntactic analysis is impossible. Semantic interpretation is viewed as a process operating on a sequence of messages characterizing local grammatical relations among phrases, rather than as a recursive tree walk over a globaUy complete and coherent parse tree. The combination of incremental semantic interpretation and statistical control of the parsing process makes it feasible to reconstruct local grammatical relations with substantial accuracy, even when a global parse cannot be obtained. Grammatical relations provide the interface between syntactic processing and semantic interpretation, and standard global parsing is viewed as merely one way to obtain evidence for the existence of such grammatical relations in an input string. This focus on grammatical relations leads to substantial simplification of both grammar and semantic rules, and will facilitate our ultimate aim of acquiring syntactic, semantic and lexical knowledge by largely