<?xml version="1.0" standalone="yes"?>
<Paper uid="C04-1171">
  <Title>A System for Generating Descriptions of Sets of Objects in a Rich Variety</Title>
  <Section position="3" start_page="0" end_page="0" type="intro">
    <SectionTitle>
2 Motivation
</SectionTitle>
    <Paragraph position="0"> Identifying sets of objects originally followed the incremental algorithm (Dale and Reiter 1995), as in (Bateman 1999), (Stone 2000) and (Krahmer et al. 2003), with limited coverage, since only few attributes typically apply to all intended referents and to none of the potential distractors. Therefore, van Deemter (2002) has extended the set of descriptors to boolean combinations of attributes, including negations. Unfortunately, when applying the incremental strategy, this may lead to the inclusion of too many redundant descriptors in the final specification. This deficit disappeared using an exhaustive search (Gardent 2002), but run-time then increases considerably. Mediating between these two extreme search paradigms, we have developed a best-first searching algorithm that avoids the major deficit of the incremental approach (Horacek 2003). Since its intermediate results can also be used as partial descriptions, we build on the flexibility of this new algorithm to extend its expressive capabilities. In addition, we further enhance its efficiency-seeking measures.</Paragraph>
    <Paragraph position="1"> These extensions attack the deficits previous algorithms share, according to (Horacek 2004): * Expressions produced may become lengthy: for identifying sets of vehicles in the scenario in Figure 1, we have obtained non-redundant specifications with up to 8 descriptors.</Paragraph>
    <Paragraph position="2"> * Specifications may contain some disjunctions, frequently causing the production of structurally ambiguous expressions (Gardent 2002) &amp;quot;trucks and sportscars which are white or in the center&amp;quot; referring to x1, x5, x11 (Figure 1).</Paragraph>
    <Paragraph position="3"> We avoid these deficits by not restricting boolean expressions to a form with conjunctions as top level operators, as others always do. This allows us to incorporate descriptions of objects to be excluded, to produce enumerations and compositions of descriptions of subsets of the intended referents, and to build compositions of increasingly restricting descriptions of these referents.</Paragraph>
    <Paragraph position="5"/>
  </Section>
class="xml-element"></Paper>