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<Paper uid="P02-1054">
  <Title>Is It the Right Answer? Exploiting Web Redundancy for Answer Validation</Title>
  <Section position="2" start_page="0" end_page="0" type="intro">
    <SectionTitle>
1 Introduction
</SectionTitle>
    <Paragraph position="0"> Open domain question-answering (QA) systems search for answers to a natural language question either on the Web or in a local document collection. Different techniques, varying from surface patterns (Subbotin and Subbotin, 2001) to deep semantic analysis (Zajac, 2001), are used to extract the text fragments containing candidate answers. Several systems apply answer validation techniques with the goal of filtering out improper candidates by checking how adequate a candidate answer is with respect to a given question. These approaches rely on discovering semantic relations between the question and the answer. As an example, (Harabagiu and Maiorano, 1999) describes answer validation as an abductive inference process, where an answer is valid with respect to a question if an explanation for it, based on background knowledge, can be found.</Paragraph>
    <Paragraph position="1"> Although theoretically well motivated, the use of semantic techniques on open domain tasks is quite expensive both in terms of the involved linguistic resources and in terms of computational complexity, thus motivating a research on alternative solutions to the problem.</Paragraph>
    <Paragraph position="2"> This paper presents a novel approach to answer validation based on the intuition that the amount of implicit knowledge which connects an answer to a question can be quantitatively estimated by exploiting the redundancy of Web information. The hypothesis is that the number of documents that can be retrieved from the Web in which the question and the answer co-occur can be considered a significant clue of the validity of the answer. Documents are searched in the Web by means of validation patterns, which are derived from a linguistic processing of the question and the answer. In order to test this idea a system for automatic answer validation has been implemented and a number of experiments have been carried out on questions and answers provided by the TREC-2001 participants. The advantages of this approach are its simplicity on the one hand and its efficiency on the other.</Paragraph>
    <Paragraph position="3"> Automatic techniques for answer validation are of great interest for the development of open domain QA systems. The availability of a completely automatic evaluation procedure makes it feasible QA systems based on generate and test approaches.</Paragraph>
    <Paragraph position="4"> In this way, until a given answer is automatically Computational Linguistics (ACL), Philadelphia, July 2002, pp. 425-432. Proceedings of the 40th Annual Meeting of the Association for proved to be correct for a question, the system will carry out different refinements of its searching criteria checking the relevance of new candidate answers. In addition, given that most of the QA systems rely on complex architectures and the evaluation of their performances requires a huge amount of work, the automatic assessment of the relevance of an answer with respect to a given question will speed up both algorithm refinement and testing.</Paragraph>
    <Paragraph position="5"> The paper is organized as follows. Section 2 presents the main features of the approach. Section 3 describes how validation patterns are extracted from a question-answer pair by means of specific question answering techniques. Section 4 explains the basic algorithm for estimating the answer validity score.</Paragraph>
    <Paragraph position="6"> Section 5 gives the results of a number of experiments and discusses them. Finally, Section 6 puts our approach in the context of related works.</Paragraph>
  </Section>
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