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<Paper uid="C04-1069">
  <Title>Document Re-ranking Based on Automatically Acquired Key Terms in Chinese Information Retrieval</Title>
  <Section position="2" start_page="0" end_page="0" type="intro">
    <SectionTitle>
1 Introduction
</SectionTitle>
    <Paragraph position="0"> Information retrieval (IR) is used to retrieve relevant documents from a large document set for a given query where the query is a simple description by natural language. In most practical situations, users concern more on the precision of top ranking documents than recall because users want to acquire relevant information from the top ranking documents.</Paragraph>
    <Paragraph position="1"> Traditionally, IR system uses a one-stage or a two-stage mechanism to retrieve relevant documents from document set. For one stage mechanism, IR system only does an initial retrieval. For two-stage mechanism, besides the initial retrieval, IR system will make use of the initial ranking documents to automatically do query expansion to form a new query and then use the new query to retrieve again to get the final ranking documents. The effectiveness of query expansion mainly depends on the precision of top N (N&lt;50) ranking documents in initial retrieval because almost all proposed automatic query expansion algorithms make use of the information in the top N retrieved.</Paragraph>
    <Paragraph position="2"> Figure 1 demonstrates the general processes of a two-stage IR system.</Paragraph>
    <Paragraph position="3"> In this paper, we propose a method to improve the precision of top N ranking documents by reordering the initially retrieved documents in the initial retrieval. To reorder documents, we first automatically extract Global Key Terms from the document set, then use the extracted Global Key Terms to identify Local Key Terms in a single document or query topic, finally we make use of the Local Key Terms in queries and documents to reorder the initial ranking documents.</Paragraph>
    <Paragraph position="4"> Although our method is general and can apply to any languages, in this paper we'll only focus on the research on Chinese IR system.</Paragraph>
    <Paragraph position="5"> F i g . 1 T r a d i t i o n a l P r o c e s s o f t w o - s t a g e s I R  The rest of this paper is organized as following. In section 2, we give an overall introduction of our proposed method. In section 3, we talk about what are Global Key Terms and what are Local Key Terms and how to acquire them. In section 4, we describe how these terms apply to Chinese IR system to improve the precision and quality of IR system. In section 5, we evaluate the performance of our proposed method and give some result analysis. In section 6, we present the conclusion and some future work.</Paragraph>
  </Section>
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