Prepositional Phrase Disambiguation

Abstract

Syntactic ambiguity is a notoriously difficult problem. In this chapter we show that lexical level commonsense knowledge can be used, in conjunction with syntactic and preposition-specific knowledge, to handle 99% of the post-verbal prepositional phrase ambiguity in a corpus of geography text.⁸ The method discards spurious syntactic ambiguities introduced by post-verbal prepositional phrase attachment during parsing. A completely naive parser will generate three parses for sentences of the form NP-V-NP-PP. The prepositions alone are insufficiently precise in meaning to guide selection among competing parses. The method employs commonsense knowledge of concepts in preference strategies which appeal to the meaning of the preposition combined with information about the verbs and nouns associated with it drawn from the text and from the generic and ontological databases. These determine which syntactic structures generated by a semantically naive parser are commonsensically plausible. The method was successful in 93% of cases tested.