Generalized phrase structure grammar

Generalised Phrase Structure Grammar (GPSG) is a theory of syntax and semantics initially developed by Gerald Gazdar. The theory is in part a reaction to the postulation of syntactic transformations. GPSG attempts to model natural language grammars as context-free grammars, making use of a sophisticated system of feature structures, "meta-rules" (rules generating the rules of a context-free grammar) and a highly developed semantic theory. These features of the theory are claimed to make transformations redundant. GPSG has developed into Head-driven phrase structure grammar.