tailieunhanh - Báo cáo khoa học: "Coordinate Noun Phrase Disambiguation in a Generative Parsing Model"

In this paper we present methods for improving the disambiguation of noun phrase (NP) coordination within the framework of a lexicalised history-based parsing model. As well as reducing noise in the data, we look at modelling two main sources of information for disambiguation: symmetry in conjunct structure, and the dependency between conjunct lexical heads. Our changes to the baseline model result in an increase in NP coordination dependency f-score from to , which represents a relative reduction in f-score error of 13%. . | Coordinate Noun Phrase Disambiguation in a Generative Parsing Model Deirdre Hogan Computer Science Department Trinity College Dublin Dublin 2 Ireland dhogan@ Abstract In this paper we present methods for improving the disambiguation of noun phrase NP coordination within the framework of a lexicalised history-based parsing model. As well as reducing noise in the data we look at modelling two main sources of information for disambiguation symmetry in conjunct structure and the dependency between conjunct lexical heads. Our changes to the baseline model result in an increase in NP coordination dependency -score from to which represents a relative reduction in -score error of 13 . 1 Introduction Coordination disambiguation is a relatively little studied area yet the correct bracketing of coordination constructions is one of the most difficult problems for natural language parsers. In the Collins parser Collins 1999 for example dependencies involving coordination achieve an -score as low as by far the worst performance of all dependency types. Take the phrase busloads of executives and their wives taken from the WSJ treebank . The coordinating conjunction CC and and the noun phrase their wives could attach to the noun phrase executives as illustrated in Tree 1 Figure 1. Alternatively their wives could be incorrectly conjoined to the noun phrase busloads of executives as in Tree 2 Figure 1. Now at the National Centre for Language Technology Dublin City University Ireland. 680 As with PP attachment most previous attempts at tackling coordination as a subproblem of parsing have treated it as a separate task to parsing and it is not always obvious how to integrate the methods proposed for disambiguation into existing parsing models. We therefore approach coordination disambiguation not as a separate task but from within the framework of a generative parsing model. As noun phrase coordination accounts for over 50 of coordination dependency .