This paper presents link analysis based on rhetorical relations with the aim of performing extractive summarization for multiple documents. We first extracted sentences with salient terms from individual document using statistical model. We then ranked the extracted sentences by measuring their relative importance according to their connectivity among the sentences in the document set using PageRank based on the rhetorical relations. The rhetorical relations were examined beforehand to determine which relations are crucial to this task, and the relations among sentences from documents were automatically identified by SVMs. We used the relations to emphasize important sentences during sentence ranking by PageRank and eliminate redundancy from the summary candidates. Our framework omits fully annotated sentences by humans and the evaluation results show that the combination of PageRank along with rhetorical relations does help to improve the quality of extractive summarization.

This paper is intended as an investigation of scientific discoveries from a philosophical point of view. In the first half of this century, most of philosophers rather concentrated on the logical analysis of science and set the problem of discovery aside. Logical positivists distinguished a context of discovery from a context of justification and excluded the former from their analysis of scientific theories. Although Popper criticized their inductivism and suggested methodological falsificationism, he also left the elucidation of discovery to psychological inquiries. The problem of scientific discovery was proprely treated for the first time by the "New Philosophy of Science" school in the 1960's. Hanson reevaluated the method of "retroduction" on the basis of Peirce's logical theory and analysed Kepler's astronomical discovery in detail as a typical application of it. Kuhn's theory of paradigm located discoveries in the context of scientific revolutions. Moreover, he paid attention to the function of metaphor in scientific discoveries. Metaphorical use of existing terms and concepts to overcome theoretical difficulties often plays a decisive role in developping new ideas. In the period of scientific revolution, theoretical metaphors can open up new horizons of scientific research by way of juxtapositions of heterogeneous concepts. To explicate such a complicated situation we need the "rhetoric" of science rather than the "logic" of science.