Robust parsing for spoken language systems

A recent extension to the MIT ATIS (Air Travel Information Service) system, which allows it to answer a question when a full linguistic analysis fails is described. Robust parsing is applied only after a full analysis has failed, and it involves the two stages of (1) parsing a set of phrases and clauses, and (2) gluing them together to obtain a single semantic frame encoding the full meaning of the sentence. In a recent evaluation, less than two-thirds of the sentences analyzed yielded a full parse, but the overwhelming majority of the remaining sentences were analyzed correctly by the robust parsing scheme. When text input was replaced by recognizer outputs, even though the recognizer produced greater than 50% sentence error rate, the drop in score (%correct-%incorrect) was only 10 percentage points. This indicates that most of the recognizer errors are harmless in terms of meaning analysis, as long as a robust mechanism for accounting for the parsable phrases is in place