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Báo cáo khoa học: "An Unsupervised Approach to Prepositional Phrase Attachment using Contextually Similar Words"

Prepositional phrase attachment is a common source of ambiguity in natural language processing. We present an unsupervised corpus-based approach to prepositional phrase attachment that achieves similar performance to supervised methods. Unlike previous unsupervised approaches in which training data is obtained by heuristic extraction of unambiguous examples from a corpus, we use an iterative process to extract training data from an automatically parsed corpus. | An Unsupervised Approach to Prepositional Phrase Attachment using Contextually Similar Words Patrick Pantel and Dekang Lin Department of Computing Science University of Alberta1 Edmonton Alberta T6G 2H1 Canada ppantel lindek @cs.ualberta.ca Abstract Prepositional phrase attachment is a common source of ambiguity in natural language processing. We present an unsupervised corpus-based approach to prepositional phrase attachment that achieves similar performance to supervised methods. Unlike previous unsupervised approaches in which training data is obtained by heuristic extraction of unambiguous examples from a corpus we use an iterative process to extract training data from an automatically parsed corpus. Attachment decisions are made using a linear combination of features and low frequency events are approximated using contextually similar words. Introduction Prepositional phrase attachment is a common source of ambiguity in natural language processing. The goal is to determine the attachment site of a prepositional phrase in a sentence. Consider the following examples 1. Mary ate the salad with a fork. 2. Mary ate the salad with croutons. In both cases the task is to decide whether the prepositional phrase headed by the preposition with attaches to the noun phrase NP headed by salad or the verb phrase VP headed by ate. In the first sentence with attaches to the VP since Mary is using a fork to eat her salad. In sentence 2 with attaches to the NP since it is the salad that contains croutons. Formally prepositional phrase attachment is simplified to the following classification task. Given a 4-tuple of the form V N1 P N2 where V is the head verb N1 is the head noun of the object of V P is a preposition and N2 is the head noun of the prepositional complement the goal is to classify as either adverbial attachment attaching to V or adjectival attachment attaching to N1 . For example the 4-tuple eat salad with fork has target classification V. In this paper we present .