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<Paper uid="C02-1042">
  <Title>Using Knowledge to Facilitate Factoid Answer Pinpointing</Title>
  <Section position="2" start_page="0" end_page="0" type="intro">
    <SectionTitle>
1. Introduction
</SectionTitle>
    <Paragraph position="0"> The TREC evaluations of QA systems (Voorhees, 1999) require answers to be drawn from a given source corpus. Early QA systems used a simple filtering technique, question word density within a fixed n-word window, to pinpoint answers. Robust though this may be, the window method is not accurate enough. In response, factoid question answering systems have evolved into two types: * Use-Knowledge: extract query words from the input question, perform IR against the source corpus, possibly segment resulting documents, identify a set of segments containing likely answers, apply a set of heuristics that each consults a different source of knowledge to score each candidate, rank them, and select the best (Harabagiu et al., 2001; Hovy et al., 2001; Srihari and Li, 2000; Abney et al., 2000).</Paragraph>
    <Paragraph position="1"> * Use-the-Web: extract query words from the question, perform IR against the web, extract likely answer-bearing sentences, canonicalize the results, and select the most frequent answer(s). Then, for justification, locate examples of the answers in the source corpus (Brill et al., 2001; Buchholz, 2001).</Paragraph>
    <Paragraph position="2"> Of course, these techniques can be combined: the popularity ratings from Use-the-Web can also be applied as a filtering criterion (Clarke et al., 2001), or the knowledge resource heuristics can filter the web results. However, simply going to the web without using further knowledge (Brill et al., 2001) may return the web's majority opinions on astrology, the killers of JFK, the cancerous effects of microwave ovens, etc.--fun but not altogether trustworthy. In this paper we describe the range of filtering techniques our system Webclopedia applies, from simplest to most sophisticated, and indicate their impact on the system.</Paragraph>
  </Section>
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