Catalogue of Artificial Intelligence Techniques


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Unification Grammars

Keywords: terms

Categories: Natural Language

Author(s): Pete Whitelock

Unification Grammar (UG) is the collective name for a group of linguistic formalisms and theories based on the idea of linguistic objects as partial information structures. Most UGs assume that linguistic objects are graph structures--sets of pairs of feature names and feature values, with the values possibly complex (see entry for Feature Structures). The primary operation for combining such structures is Graph Unification. However, grammar formalisms based on term unification, such as Definite Clause Grammars, are closely allied, even though term and graph unification were introduced independently (by Robinson and Kay respectively). As well as providing a sound understanding of how features in the sense of traditional grammar should behave, UGs appear to offer great flexibility in their computational properties, due to the monotonic (order-independent) nature of the operation of unification. Current research issues in UGs include the definition of more expressive feature logics for describing linguistic objects, and efficient algorithms for computing with these.



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