Integrated Control of Chart Items for Error Repair

This paper describes a system that performs hierarchical error repair for ill-formed sentences, with heterarchical control of chart items produced at the lexical, syntactic, and semantic levels. The system uses an augmented context-free grammar and employs a bidirectional chart parsing algorithm. The system is composed of four subsystems: for lexical, syntactic, surface case, and semantic processing. The subsystems are controlled by an integrated-agenda system. The system employs a parser for well-formed sentences and a second parser for repairing single error sentences. The system ranks possible repairs by penalty scores which are based on both grammar-dependent factors (e.g. the significance of the repaired constituent in a local tree) and grammar-independent factors (e.g. error types). This paper focuses on the heterarchical processing of integrated-agenda items (i.e. chart items) at three levels, in the context of single error recovery