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<Paper uid="W05-1623">
  <Title>Reversibility and Re-usability of Resources in NLG and Natural Language Dialog Systems</Title>
  <Section position="8" start_page="0" end_page="0" type="concl">
    <SectionTitle>
6 Conclusion and Further Work
</SectionTitle>
    <Paragraph position="0"> We have developed a formal description of reversibility for NLDSs, using deflnitions for program systems, system relations, and system resources. Based on these definitions, we have presented a classiflcation of reversible NLDSs in general and NLG systems in particular. Our classiflcation extends previous approaches in three dimensions: First, it covers static and dynamic reversibility, second, it considers algorithmic and data reversibility, and third, it takes the difierent resources of a dialog system into account.</Paragraph>
    <Paragraph position="1"> The 6-tuple used in our classiflcation can, of course, be extended to incorporate difierent linguistic and pragmatic resources, should they prove useful for an NLDS.</Paragraph>
    <Paragraph position="2"> However, we identifled the set of resources mentioned above by thorough investigation of existing systems based on the results presented in [Maier, 1999] for text planning; presently, we do not think we need additional ones.</Paragraph>
    <Paragraph position="3"> Unfortunately, our deflnition of reversibility does not yet completely re ect all aspects of current NLDSs: For example, it does not cover systems where preprocessing and runtime programs cannot be clearly separated, because such systems allow a exible choice for a given resource and/or algorithm to be computed beforehand (by preprocessing) or at runtime.7 This extended degree of dynamic has yet to be taken into account in our deflnitions.</Paragraph>
    <Paragraph position="4"> The obvious practical application of our classiflcation is twofold: First, using it in a descriptive way to analyze existing systems. Second, and more practical, using it in a normative way to further develop one's one NLDS to be as reversible as possible (i.e., to obtain a \D&amp;quot; in all six positions of the 6-tuple of reversibility types). Both applications are important, but the second is the one we are going to pursue in the near future.</Paragraph>
  </Section>
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