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<Paper uid="J83-1001">
  <Title>Paraphrasing Questions Using Given and New Information 1</Title>
  <Section position="2" start_page="0" end_page="0" type="abstr">
    <SectionTitle>
1. Introduction
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    <Paragraph position="0"> In a natural language interface to a data base query system, a paraphraser can be used to ensure that the system has correctly understood the user. Such a paraphraser has been developed as part of the CO-OP system (Kaplan 1979). In CO-OP, an internal representation of the user's question is passed to the paraphraser, which then generates a new version of the question for the user. Upon seeing the paraphrase, the user has the option of rephrasing her/his question before the system attempts to answer it. Thus, if the question was not interpreted correctly, the error can be caught before a possibly lengthy search of the data base is initiated. Furthermore, the user is assured that the answer she/he receives is an answer to the question asked and not to a deviant version of it.</Paragraph>
    <Paragraph position="1"> The idea of using a paraphraser in the above way is not new. To date, other systems have used canned templates to form paraphrases, filling in empty slots in the pattern with information from the user's question (Waltz 1978, Codd 1978). In CO-OP, a transformational grammar is used to generate the paraphrase from an internal representation of the question.</Paragraph>
    <Paragraph position="2"> Moreover, the CO-OP paraphraser generates a question that differs in a meaningful way from the original question. It makes use of a distinction between given 1 This work was carried out in the Department of Computer and Information Science, The University of Pennsylvania. It was partially supported by an IBM Fellowship, and by NSF grants MCS 78-08401 and MCS 79-19171.</Paragraph>
    <Paragraph position="3"> and new information to indicate to the user the existential presuppositions made in her/his question.</Paragraph>
    <Paragraph position="4"> 2. Overview of the CO-OP System The CO-OP system is aimed at infrequent users of data base query systems. These casual users are likely to be unfamiliar with computer systems and unwilling to invest the time needed to learn a formal query language. Being able to converse naturally in English enables such persons to tap the information available in a data base.</Paragraph>
    <Paragraph position="5"> In order to allow the question-answering process to proceed naturally, CO-OP follows some of the &amp;quot;cooperative principles&amp;quot; of conversation (Grice 1975). In particular, the system attempts to find meaningful answers to failed questions by addressing any incorrect assumptions the questioner may have made in her/his question. When the direct response to a question would be simply &amp;quot;no&amp;quot; or &amp;quot;none&amp;quot;, CO-OP gives a more informative response by correcting the questioner's mistaken assumptions.</Paragraph>
    <Paragraph position="6"> The false assumptions that CO-OP corrects are the existential presuppositions of the questions. 2 Since these presuppositions can be computed from the surface structure of the question, a large store of semantic knowledge for inferencing purposes is not needed. 2 For example, in the question &amp;quot;Which users work on projects sponsored by NASA?&amp;quot;, the speaker makes the existential presupposition that there are projects sponsored by NASA.</Paragraph>
    <Paragraph position="7"> Copyright 1983 by the Association for Computational Linguistics. Permission to copy without fee all or part of this material is granted provided that the copies are not made for direct commercial advantage and the Journal reference and this copyright notice are included on the first page. To copy otherwise, or to republish, requires a fee and/or specific permission. 0362-613X/83/010001 - 10503.00 American Journal of Computational Linguistics, Volume 9, Number 1, January-March 1983 1 Kathleen R. McKeown Paraphrasing Questions Using Given and New Information In fact, a lexicon and data base schema are the only items that contain domain-specific information. Consequently, the CO-OP system is a portable one; a change of data base requires that only these two knowledge sources be modified.</Paragraph>
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