This paper describes a system that performs hierarchical error repair for illformed 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 integratedagenda items (i.e. chart items) at three levels, in the context of single error recovery.
Kyongho Min, William H. Wilson