tailieunhanh - Báo cáo khoa học: "EM Works for Pronoun Anaphora Resolution"

We present an algorithm for pronounanaphora (in English) that uses Expectation Maximization (EM) to learn virtually all of its parameters in an unsupervised fashion. While EM frequently fails to find good models for the tasks to which it is set, in this case it works quite well. We have compared it to several systems available on the web (all we have found so far). Our program significantly outperforms all of them. The algorithm is fast and robust, and has been made publically available for downloading | EM Works for Pronoun Anaphora Resolution Eugene Charniak and Micha Elsner Brown Laboratory for Linguistic Information Processing BLLIP Brown University Providence RI 02912 ec melsner @ Abstract We present an algorithm for pronounanaphora in English that uses Expectation Maximization EM to learn virtually all of its parameters in an unsupervised fashion. While EM frequently fails to find good models for the tasks to which it is set in this case it works quite well. We have compared it to several systems available on the web all we have found so far . Our program significantly outperforms all of them. The algorithm is fast and robust and has been made publically available for downloading. 1 Introduction We present a new system for resolving personal pronoun anaphora1. We believe it is of interest for two reasons. First virtually all of its parameters are learned via the expectationmaximization algorithm EM . While EM has worked quite well for a few tasks notably machine translations starting with the IBM models 1-5 Brown et al. 1993 it has not had success in most others such as part-of-speech tagging Meri-aldo 1991 named-entity recognition Collins and Singer 1999 and context-free-grammar induction numerous attempts too many to mention . Thus understanding the abilities and limitations of EM is very much a topic of interest. We present this work as a positive data-point in this ongoing discussion. Secondly and perhaps more importantly is the system s performance. Remarkably there are very few systems for actually doing pronoun anaphora available on the web. By emailing the corpora-list the other members of the list pointed us to 1The system the Ge corpus and the model described here can be downloaded from http download . four. We present a head to head evaluation and find that our performance is significantly better than the competition. 2 Previous Work The literature on pronominal anaphora is quite large and we cannot .