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<Paper uid="E87-1022">
  <Title>Subgrammars, Rule Classes and Control in the Rosetta Translation System *</Title>
  <Section position="7" start_page="129" end_page="129" type="concl">
    <SectionTitle>
7 Conclusion
</SectionTitle>
    <Paragraph position="0"> In section 2 we enumerated three types of problems with the free M-grammar formalism used for the development of the Rosettal and Rosetta2 systems.</Paragraph>
    <Paragraph position="1"> The first problem was the lack of structure in free Mgrammars. This was solved in section 3 by introducing a modular approach, where M-grammars are divided into subgrammars in a way that was inspired by the programming language Modula-2 on the one hand and by the notion projection from X-theory on the other hand.</Paragraph>
    <Paragraph position="2"> The second problem was that there is no way of explicitly controlling the application of rules in free M-grammars and that it is not obvious how this kind of control could be introduced in a compositional grammar, where rules may have more than one argument.</Paragraph>
    <Paragraph position="3"> The insight that was important to the solution of this problem was that application of a subgrammar comes down to following a projection path, from the imported head to the exported projection. This implies that defining control in a subgrammar comes down to specifying a set of possible sequences of rule applications, which can be done by means of a control expression, a regular expression over rule names. An important advantage of this way of controlling rule applications is that the One Grammar Principle is still obeyed: the same grammar (i.e. the same subgrammars: the same rules, the same control expressions, etc.) can be used for the compositional and the analytical definition of a language. This is proved by the formal definitions in subsection 6.2.</Paragraph>
    <Paragraph position="4"> The third problem concerned the consequences of defining the translation relation by means of isomorphic grammars. The introduction of an explicit distinction between meaningful rules and syntactic transformations in section 4 avoids unnecessary complications of the grammars without affecting the Principle of Isomorphy. Because the applicability of syntactic transformations is restrained by the control expressions, they do not cause problems with effectivity or efficiency. The introduction of rule classes gave more insight into complex translation relations. In section 5 it was shown that category mismatch problems can be handled more systematically by a combination of subgrammars and rule classes.</Paragraph>
  </Section>
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