The termphrase structure grammar was originally introduced byNoam Chomsky as the term forgrammar studied previously byEmil Post andAxel Thue (Post canonical systems). Some authors, however, reserve the term for more restricted grammars in theChomsky hierarchy:context-sensitive grammars orcontext-free grammars. In a broader sense, phrase structure grammars are also known asconstituency grammars. The defining character of phrase structure grammars is thus their adherence to the constituency relation, as opposed to the dependency relation ofdependency grammars.
In 1956, Chomsky wrote, "A phrase-structure grammar is defined by a finite vocabulary (alphabet) Vp, and a finite set Σ of initial strings in Vp, and a finite set F of rules of the form: X → Y, where X and Y are strings in Vp."[1]
Inlinguistics, phrase structure grammars are all those grammars that are based on the constituency relation, as opposed to the dependency relation associated with dependency grammars; hence, phrase structure grammars are also known as constituency grammars.[2] Any of several related theories for theparsing of natural language qualify as constituency grammars, and most of them have been developed from Chomsky's work, including
Further grammar frameworks and formalisms also qualify as constituency-based, although they may not think of themselves as having spawned from Chomsky's work, e.g.
