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<Paper uid="W06-1409">
  <Title>measuring the benefits for readers</Title>
  <Section position="4" start_page="55" end_page="55" type="intro">
    <SectionTitle>
2 Hierarchical domains
</SectionTitle>
    <Paragraph position="0"> Existing work on GRE tends to focus on fairly simple domains, dominated by one-place properties. When relations (i.e., two-place properties) are taken into account at all (e.g., Dale and Haddock 1991, Krahmer and Theune 2002), the motivating examples are kept so small that it is reasonable to assume that speaker and hearer know all the relevant facts in advance. Consequently, search is not much of an issue (i.e., resolution is easy): the hearer can identify the referent by simply intersecting the denotations of the properties in the description. While such simplifications permit the study of many aspects of reference, other aspects come to the fore when larger domains are considered.</Paragraph>
    <Paragraph position="1"> Interesting questions arise, for example, when a large domain is hierarchically ordered. We consider a domain to be hierarchically ordered if its inhabitants can be structured like a tree in which everything that belongs to a given node n belong to at most one of n's children, while everything that belongs to one of n's children belongs to n. Examples include countries divided into provinces which, in turn, may be divided into regions, etc.; years into months then into weeks and then into days; documents into chapters then sections then subsections; buildings into floors then rooms. Clearly, hierarchies are among our favourite ways of structuring the world.</Paragraph>
    <Paragraph position="2"> A crucial question, in all such cases, is what knowledge is shared between speaker and hearer at utterance time. It will be convenient to start by focussing on the extreme case where, before the start of resolution, knows nothing about the domain. When the utterance is made, the hearer's blindfold is removed, so to speak, and resolution can start. No similar assumption about the speaker is made: we assume that the speaker knows everything about the domain, and that he knows that the hearer can achieve the same knowledge. Many of our examples will be drawn from a simple model of a University campus, structured into buildings and rooms; the intended referent will often be a library located in one of the rooms. The location of the library is not known to the hearer, but it is known to the speaker. Each domain entity r will be  associated with a TYPE (e.g., the type 'room'), and with some additional attributes such as its ROOM NUMBER or NAME, and we will assume that it is always possible to distinguish r from its siblings in the tree structure by using one or more of these properties. (For example, 'R.NUMBER=102' identifies a room uniquely within a given building) 1.</Paragraph>
  </Section>
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