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<Paper uid="C00-1003">
  <Title>Selectional Restrictions in HPSG</Title>
  <Section position="3" start_page="0" end_page="15" type="intro">
    <SectionTitle>
1_ Introduction
</SectionTitle>
    <Paragraph position="0"> ~lPhe term selectional restrictions refers to semantic sortal constraints imposed on the 1)ar ticipants of linguistic constructions. Selectional restrictions arc invoked, for example, to account tbr the oddity of (1) and (3) (cf. (2) and (4)).</Paragraph>
    <Paragraph position="1">  (1) ?Tom ate a keyboard.</Paragraph>
    <Paragraph position="2"> (2) Tom ate a banana.</Paragraph>
    <Paragraph position="3"> (3) ?Tom repaired the technician.</Paragraph>
    <Paragraph position="4"> (4) Tom repaired the keyboard.</Paragraph>
    <Paragraph position="5">  ~IPo account tbr (1) and (2), one would typically introduce a constraint requiring the object of &amp;quot;to eat&amp;quot; to denote an edible entity. The oddity of (1) can then be attributed to a violation of this constraint, since keyboards are typically not edible. Silnilarly, in (3) and (4) one could postulate that &amp;quot;to repair&amp;quot; can only be used with objects denoting artifacts. This constraint is violated by (3), because technicians are typically persons, and persons are not artifacts.</Paragraph>
    <Paragraph position="6"> We note that selectional restrictions attempt to capture contextually-dei)endent constraints on interpretation. There is nothing inherently wrong with (1), and one can think of special contexts (e.g. where Tom is a circus pertbrmer whose act includes gnawing on comtmter peripherals) where (1) is felicitous. The oddity of (1) is due to the fact that in most contexts l)eople do not eat keyboards. Similarly, (3) is ti;licitous in a science-fiction context where the technician is a robot, |rot not in most usual contexts. Selectional restrictions are typically used to capture flints about tlm world which are genc.r~lly, but not necessarily, true.</Paragraph>
    <Paragraph position="7"> In w~rious forms, selectional restrictions have been used tbr many years, and their limitations are well-known (Allen, 1995). For example, they cmmot account tbr lnetaphoric uses of language (e.g. (5)), and they run into 1,roblen,s in negated sentences (e.g. unlike (1), there is nothing odd about (6)).</Paragraph>
    <Paragraph position="8">  (5) My car drinks gasoline.</Paragraph>
    <Paragraph position="9"> (6) Tom cannot cat a keyboard.</Paragraph>
    <Paragraph position="10">  Despite their limitations, selectional restrictions have proven very useflfl in practical applications, and they have been employed in several large-scale natural language understanding systems (Martin et al., 1086) (Alshawi, 1992). Apart fl'om blocking pragmatically ilMbrmed sentences like (1) and (3), selectional restrictions can also be used in word sense disanfl)iguation, syntactic dismnbiguation, and anaphora  resolution. In (7), for example, tile '))~qnter&amp;quot; refers to at computer peripheral, while in (8) it refers to a person. The correct sense of &amp;quot;printer&amp;quot; can be chosen in each case by requiring the object of &amp;quot;to repair&amp;quot; to denote an artifact, and the subject of &amp;quot;to call&amp;quot; (when referring to a phone call) to denote a person.</Paragraph>
    <Paragraph position="11"> (7) Tom repaired the printer.</Paragraph>
    <Paragraph position="12"> (8) The printer called this mornfilg.</Paragraph>
    <Paragraph position="13"> Silnilarly, (9) is from a syntactic point of view potentially ambiguous: the relative clause may refer either to the departments or the employees. The correct reading can be chosen by specifying that the subject of &amp;quot;retire&amp;quot; (the relativised nominal in this case) must denote a person.</Paragraph>
    <Paragraph position="14"> (9) List tile employees of the overseas departnlents that will retire next year.</Paragraph>
    <Paragraph position="15"> Given tile value of selectional restrictions in t)ractical applications, we explore how they can be utilised in the HPS~ theory (Pollard and Sag, 1994), assuming that the reader is familiar with HPSG. Onr proposals are based on experience obtained from using IIPSG in a natural language database interface (Androutsot)oulos et al., 1998) and a dialogue system for a mobile robot. To the best of our knowledge, selectional restrictions have not been explored so far in the context of HPSG.</Paragraph>
    <Paragraph position="16"> We note that, although they often exploit similar techniques (e.g. semantic sort hierarchies), selectional restrictions costitnte a different topic from linking theories (Davis, 1996). Roughly speaking, linking theories explore the relation between thematic roles (e.g. agent, patient) and grammatical thnctions (e.g. subject, complement), while selectional restrictions attempt to account tbr the types of world entities that can fill the thematic roles.</Paragraph>
    <Paragraph position="17"> We discuss in sections 2 and 3 two ways that we have considered to incorporate selectional restrictions into HPSO. Section 4 concludes by comparing briefly the two approaches.</Paragraph>
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