TAILIEUCHUNG - Báo cáo khoa học: "Minimally Lexicalized Dependency Parsing"

Dependency structures do not have the information of phrase categories in phrase structure grammar. Thus, dependency parsing relies heavily on the lexical information of words. This paper discusses our investigation into the effectiveness of lexicalization in dependency parsing. Specifically, by restricting the degree of lexicalization in the training phase of a parser, we examine the change in the accuracy of dependency relations. Experimental results indicate that minimal or low lexicalization is sufficient for parsing accuracy. . | Minimally Lexicalized Dependency Parsing Daisuke Kawahara and Kiyotaka Uchimoto National Institute of Information and Communications Technology 3-5 Hikaridai Seika-cho Soraku-gun Kyoto 619-0289 Japan dk uchimoto @ Abstract Dependency structures do not have the information of phrase categories in phrase structure grammar. Thus dependency parsing relies heavily on the lexical information of words. This paper discusses our investigation into the effectiveness of lexicalization in dependency parsing. Specifically by restricting the degree of lexicalization in the training phase of a parser we examine the change in the accuracy of dependency relations. Experimental results indicate that minimal or low lexicalization is sufficient for parsing accuracy. 1 Introduction In recent years many accurate phrase-structure parsers have been developed . Collins 1999 Charniak 2000 . Since one of the characteristics of these parsers is the use of lexical information in the tagged corpus they are called lexicalized parsers . Unlexicalized parsers on the other hand achieved accuracies almost equivalent to those of lexicalized parsers Klein and Manning 2003 Matsuzaki et al. 2005 Petrov et al. 2006 . Accordingly we can say that the state-of-the-art lexicalized parsers are mainly based on unlexical grammatical information due to the sparse data problem. Bikel also indicated that Collins parser can use bilexical dependencies only of the time the rest of the time it backs off to condition one word on just phrasal and part-of-speech categories Bikel 2004 . This paper describes our investigation into the effectiveness of lexicalization in dependency parsing 205 instead of phrase-structure parsing. Usual dependency parsing cannot utilize phrase categories and thus relies on word information like parts of speech and lexicalized words. Therefore we want to know the performance of dependency parsers that have minimal or low lexicalization. Dependency trees have been used in a .

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