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<Paper uid="E93-1003">
  <Title>Experiments in Reusability of Grammatical Resources</Title>
  <Section position="4" start_page="18" end_page="19" type="concl">
    <SectionTitle>
3 Conclusion
</SectionTitle>
    <Paragraph position="0"> Our experiments have demonstrated that migrations of various sorts can be performed with a reasonable degree of success.</Paragraph>
    <Paragraph position="1">  As regards the general questions about migration posed at the beginning, we can formulate some (partial) answers.</Paragraph>
    <Paragraph position="2"> * Successful migration obviously involves more than just I/O equivalence of source and target descriptions. One also looks for similar degrees of 'descriptive adequacy' (i.e. compactness, perspicuity, maintainability etc.). Clearly reusability implies usability. However, this is not an absolute property, and a small loss of such properties can be acceptable. It is clear, however, that the loss of maintainability that we have experienced in some of the migration activities above is unacceptable.</Paragraph>
    <Paragraph position="3"> * How conceptually close must source and target be for migration to be successful? We have seen that in principle it is possible to migrate resources across certain formal/ideological divides -- for example, from ttPSG, which has no rules, but uses types extensively, to ALE\]', which has a weaker type system, and is CF-PSG rule based; and from LFG (which does not use typed feature structures) to ALEP. The migration of IIPSG specifications into the rule based ALEP entails a considerable degree of fragmentation and particularisation of the linguistic information encoded in the original specification. To a certain extent this can be recaptured if the target formalism provides an integrated template facility which is not restricted to simple lexical expansion. We have also suggested that good documentation can alleviate the effects of distance  between formalisms.</Paragraph>
    <Paragraph position="4"> * With respect to the migration of descriptions using richer expressive devices, it is clear that it is sometimes possible to dispense with the richer devices, and that some descriptions couched in richer formalims do not use them in any crucial way. The HPSG conversion experiment, however, has clearly shown that for set valued features, and operations on sets, a naive encoding is simply unacceptable.</Paragraph>
    <Paragraph position="5"> * We have seen that the effect of non-monotonic devices in a source formMism can be serious, especially when it is combined with unclear rule semantics (c.f. the ETS conversion experiment).</Paragraph>
    <Paragraph position="6"> However, the existence of an 'object' formalism where the non-monotonic devices are compiled out (like in the case of the ALVEY grammars) is an asset, and again, good documentation helps.</Paragraph>
    <Paragraph position="7"> Particularly in the case of the LFG conversion experiment it became clear that often there is a crucial difference between the availability of certain non-monotonic devices and their actuM use. E.g. it was found that existential constraints are often used to express subtype information. If the type system is rich enough, this information can be modelled in the type system specification in the target formalism.</Paragraph>
    <Paragraph position="8"> * As expected, we have found macros and pre-processors a useful tool, especially in the semi-automatic migration of lexical resources. In order to approximate a principles based style of linguistic description like in HPSG the target formalism should be extended with an integrated template facility which determines satisfiability of templates (principles) in terms of unification.</Paragraph>
  </Section>
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