Tree-Adjoining Grammar

A tree-adjoining grammar (TAG) is a type of formal grammar developed by linguists to increase the expressiveness and address some of the shortcomings of context-free grammars. Whereas conventional generative grammars are defined in terms of a set of rules that transform one string to another, tree-adjoining grammars are defined in terms of a set of rules that transform one parse tree to another. By defining transformations on the basis of parse trees rather than strings, the rules of the grammar can take into consideration a larger amount of structural context and thereby more accurately model human speech patterns.