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<Paper uid="W05-1607">
  <Title>A context-dependent algorithm for generating locative expressions in physically situated environments</Title>
  <Section position="4" start_page="0" end_page="0" type="intro">
    <SectionTitle>
2 Data
</SectionTitle>
    <Paragraph position="0"> When one considers that the English lexicon of spatial prepositions numbers above eighty members (not considering compounds such as right next to) [Landau, 1996], the combinatorial aspect of relational scene model construction becomes apparent. It should be noted that for our purposes, the situation is somewhat ameliorated by the fact that a distinction can be made between static and dynamic prepositions: static prepositions primarily2 denote the location of an object, dynamic prepositions primarily denote the path of an object [Jackendoff, 1983; Herskovits, 1986], see (2). However, even focusing exclusively on the set of static prepositions does not remove the combinatorial issues effecting the construction of a scene model.</Paragraph>
    <Paragraph position="1"> (2) a. the tree is behind [static] the house b. the man walked across [dynamic] the road In general, the set of static prepositions can be decomposed into two sets called topological and projective. Topological prepositions are the category of prepositions referring to a region that is proximal to the landmark; e.g., at, near, etc.</Paragraph>
    <Paragraph position="2"> Often, the distinctions between the semantics of the different topological prepositions is based on pragmatic contraints, for example the use of at licences the trajector to be in contact with the landmark, by contrast the use of near does not.</Paragraph>
    <Paragraph position="3"> Projective prepositions describe a region projected from the landmark in a particular direction, the specification of the direction is dependent on the frame of reference being used; e.g., to the right of, to the left of, etc.</Paragraph>
    <Paragraph position="4"> The semantics of static prepositions exhibit both qualitative and quantitative properties. The qualitative aspect of their semantics is evident when they are used to denote an object by contrasting its location with the distractor objects location. Taking Figure 1 as a visual context the locative expression the circle on the left of the square exhibits the contrastive semantics of a projective preposition. Only one of the circles in the scene is located in the region to the right of the square. Taking Figure 2 as a visual context the locative expression the circle near the black square illustrates the contrastive semantics of a topological preposition. Again, of the two circles in the scene only one of them may be appropriately described as being near the black square, the other circle is more appropriately described as being near the white square. The quantitative aspect of the semantics of static prepositions is evident when they denote an object using a relative scale. In the context provided by Figure 3 the locative the circle to the right of the square exhibits the relative semantics of a projective preposition. Although both the circles are located to the 2Static prepositions can be used in dynamic contexts, e.g. the man ran behind the house, and dynamic prepositions can be used in static ones, e.g. the tree lay across the road.</Paragraph>
    <Paragraph position="5"> right of the square it is possible to adjudicate between them based on their location in the region. The relative semantics of a topological preposition can also be illustrated using Figure 3. A description such as the circle near the square could be applied to either circle if the other circle was not present.</Paragraph>
    <Paragraph position="6"> However, when both are present it is possible to interpret the reference based on their relative proximity to the landmark  tics of topological and projective prepositions.</Paragraph>
  </Section>
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