Integrated correction of ill-formed sentences

Abstract

This paper describes a system that performs hierarchical error recovery, and detects and corrects a single error in a sentence at the lexical, syntactic, and/or semantic levels. If the system is unable to repair an erroneous sentence on the assumption that it has a single error, a multiple error recovery system is invoked. The system employs a chart parsing algorithm and uses an augmented context-free grammar, and has subsystems for lexical, syntactic, surface case, and semantic processing, which are controlled by an integrated-agenda system. In the frequent case that there is a choice of possible repairs, the possible repairs are ranked by penalty scores. The penalty scores are based on grammar-dependent and grammar-independent heuristics. The grammar-independent ones involve error types, and, at the lexical level, character distance; the grammar-dependent ones involve, at the syntactic level, the significance of the repaired constituent in a local tree, and, at the semantic level, the distance between the semantic form containing the error, and normal act templates. This paper focuses on single error recovery.