tailieunhanh - Báo cáo khoa học: "Modelling the substitutability of discourse connectives"

Processing discourse connectives is important for tasks such as discourse parsing and generation. For these tasks, it is useful to know which connectives can signal the same coherence relations. This paper presents experiments into modelling the substitutability of discourse connectives. It shows that substitutability effects distributional similarity. A novel variancebased function for comparing probability distributions is found to assist in predicting substitutability. | Modelling the substitutability of discourse connectives Ben Hutchinson School of Informatics University of Edinburgh Abstract Processing discourse connectives is important for tasks such as discourse parsing and generation. For these tasks it is useful to know which connectives can signal the same coherence relations. This paper presents experiments into modelling the substitutability of discourse connectives. It shows that substitutability effects distributional similarity. A novel variancebased function for comparing probability distributions is found to assist in predicting substitutability. 1 Introduction Discourse coherence relations contribute to the meaning of texts by specifying the relationships between semantic objects such as events and propositions. They also assist in the interpretation of anaphora verb phrase ellipsis and lexical ambiguities Hobbs 1985 Kehler 2002 Asher and Las-carides 2003 . Coherence relations can be implicit or they can be signalled explicitly through the use of discourse connectives . because even though. For a machine to interpret a text it is important that it recognises coherence relations and so as explicit markers discourse connectives are of great assistance Marcu 2000 . When discourse connectives are not present the task is more difficult. For such cases unsupervised approaches have been developed for predicting relations by using sentences containing discourse connectives as training data Marcu and Echihabi 2002 Lapata and Las-carides 2004 . However the nature of the relationship between the coherence relations signalled by discourse connectives and their empirical distributions has to date been poorly understood. In particular one might wonder whether connectives with similar meanings also have similar distributions. Concerning natural language generation texts are easier for humans to understand if they are coherently structured. Addressing this a body of research has considered the problems