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<Paper uid="P02-1032">
  <Title>The Descent of Hierarchy, and Selection in Relational Semanticsa0</Title>
  <Section position="3" start_page="0" end_page="0" type="intro">
    <SectionTitle>
(MeSH, Medical Subject Headings) to determine the re-
</SectionTitle>
    <Paragraph position="0"> lations that hold between the words in noun compounds.</Paragraph>
    <Paragraph position="1"> Surprisingly, we find that we can simply use the juxtaposition of category membership within the lexical hierarchy to determine the relation that holds between pairs of nouns. For example, for the NCs leg paresis, skin numbness, and hip pain, the first word of the NC falls into the MeSH A01 (Body Regions) category, and the second word falls into the C10 (Nervous System Diseases) category. From these we can declare that the relation that holds between the words is &amp;quot;located in&amp;quot;. Similarly, for influenza patients and aids survivors, the first word falls under C02 (Virus Diseases) and the second is found in M01.643 (Patients), yielding the &amp;quot;afflicted by&amp;quot; relation. Using this technique on a subpart of the category space, we obtain 90% accuracy overall.</Paragraph>
    <Paragraph position="2"> In some sense, this is a very old idea, dating back to the early days of semantic nets and semantic grammars.</Paragraph>
    <Paragraph position="3"> The critical difference now is that large lexical resources and corpora have become available, thus allowing some of those old techniques to become feasible in terms of coverage. However, the success of such an approach depends on the structure and coverage of the underlying lexical ontology.</Paragraph>
    <Paragraph position="4"> In the following sections we discuss the linguistic motivations behind this approach, the characteristics of the lexical ontology MeSH, the use of a corpus to examine the problem space, the method of determining the relations, the accuracy of the results, and the problem of ambiguity. The paper concludes with related work and a discussion of future work.</Paragraph>
  </Section>
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