Assessing the Role of Discourse References in Entailment Inference

Proceedings of the 48th Annual Meeting of the Association for Computational Linguistics, pages 1209–1219, Uppsala, Sweden, 11-16 July 2010. c⃝2010 Association for Computational Linguistics Assessing the Role of Discourse References in Entailment Inference Shachar Mirkin, Ido Dagan Bar-Ilan University Ramat-Gan, Israel {mirkins,dagan}@cs.biu.ac.il Sebastian Pad´o University of Stuttgart Stuttgart, Germany pado@ims.uni-stuttgart.de Abstract Discourse references, notably coreference and bridging, play an important role in many text understanding applications, but their impact on textual entailment is yet to be systematically understood. On the ba- sis of an in-depth analysis of entailment instances, we argue that discourse refer- ences have the potential of substantially improving textual entailment recognition, and identify a number of research direc- tions towards this goal. 1 Introduction The detection and resolution of discourse refer- ences such as coreference and bridging anaphora play an important role in text understanding appli- cations, like question answering and information extraction. There, reference resolution is used for the purpose of combining knowledge from multi- ple sentences. Such knowledge is also important for Textual Entailment (TE), a generic framework for modeling semantic inference. TE reduces the inference requirements of many text understand- ing applications to the problem of determining whether the meaning of a given textual assertion, termed hypothesis (H), can be inferred from the meaning of certain text (T) (Dagan et al., 2006). Consider the following example: (1) T: “Not only had he developed an aversion to the President1 and politics in general, Oswald2 was also a failure with Marina, his wife. [...] Their relationship was supposedly responsible for why he2 killed Kennedy1.” H: “Oswald killed President Kennedy.” The understanding that the second sentence of the text entails the hypothesis draws on two corefer- ence relationships, namely that he is Oswald, and that the Kennedy in question is President Kennedy. However, the utilization of discourse information for such inferences has been so far limited mainly to the substitution of nominal coreferents, while many aspects of the interface between discourse and semantic inference needs remain unexplored. The recently held Fifth Recognizing Textual Entailment (RTE-5) challenge (Bentivogli et al., 2009a) has introduced a Search task, where the text sentences are interpreted in the context of their full discourse, as in Example 1 above. Accord- ingly, TE constitutes an interesting framework – and the Search task an adequate dataset – to study the interrelation between discourse and inference. The goal of this study is to analyze the roles of discourse references for textual entailment in- ference, to provide relevant findings and insights to developers of both reference resolvers and en- tailment systems and to highlight promising direc- tions for the better incorporation of discourse phe- nomena into inference. Our focus is on a manual, in-depth assessment that results in a classification and quantification of discourse reference phenom- ena and their utilization for inference. On this ba- sis, we develop an account of formal devices for incorporating discourse references into the infer- ence computation. An additional point of inter- est is the interrelation between entailment knowl- edge and coreference. …

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