A Level-Synchronous Approach to Ill-formed Sentence Parsing and Error Recovery

In this paper, a level-synchronous parsing mechanism, named Phrase-Level Building (PLB), is proposed to incorporate wide-scope contextual information for parsing illformed sentences. This mechanism regards the task of parsing a sentence as the task of building the phrase-levels for the sentence. Therefore, the wide-scope contextual information in the phrase-levels can be used to help narrow down the search space and to select the most likely partial parses. Compared with the system which uses both the stochastic context-free grammar and the heuristics of preferring the longest phrase, the proposed PLB approach improves the precision rate for brackets in the partial parse forests from 69.37% to 79.49%. The recall rate for brackets is also improved from 78.73% to 81.39%. The proposed PLB parsing method can also be used to recover errors in illformed sentences, so that more complete syntactic information can be provided in later stages. Experimental results show that 35% of the ill-formed sentences can be recovered to well-formed parses. The recall rate for brackets is also significantly improved from 68.49% to 76.60% while the precision rate for brackets is improved slightly from 79.49% to 80.69%.