Catalogue of Artificial Intelligence Techniques

   

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Meta-rules

Keywords: Meta-level Inference, Transformational Grammar

Categories: Natural Language


Author(s): Henry Thompson, Nicolas Nicolov

In linguistics, meta-rules are a way of increasing the expressive power of a grammatical formalism. Informally, a grammar with meta-rules provides two ways of specifying rules: explicitly, by adding/specifying individual rules, or implicitly, by the mechanism of meta-rules. A meta-rule is a statement of the kind `If the grammar contains a rule of a particular form, then the grammar also contains other rules whose form is systematically related to the form of the original rule.' Context-free Grammars are well suited to extension by meta-rules. Meta-rules were extensively used in Generalised Phrase Structure Grammar (GPSG). For example, in GPSG the passive construction is added to the grammar by means of the passive meta-rule which uses the pattern of the active construction. Meta-rules are not transformations (as used in Transformational Grammar). They are also to be distinguished from derived rules which are special instances of other rules and are used in GPSG to implement long-distance dependencies.


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