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The Chomsky hierarchy in the fields of formal language theory, computer science, and linguistics, is a containment hierarchy of classes of formal grammars. A formal grammar describes how to form strings from a language's vocabulary (or alphabet) that are valid according to the language's syntax.
When Noam Chomsky first formalized generative grammars in 1956, [2] he classified them into types now known as the Chomsky hierarchy. The difference between these types is that they have increasingly strict production rules and can therefore express fewer formal languages.
In automata theory, the class of unrestricted grammars (also called semi-Thue, type-0 or phrase structure grammars) is the most general class of grammars in the Chomsky hierarchy. No restrictions are made on the productions of an unrestricted grammar, other than each of their left-hand sides being non-empty.
In his work Aspects of the Theory of Syntax (1965), Noam Chomsky introduces a hierarchy of levels of adequacy for evaluating grammars (theories of specific languages) and metagrammars (theories of grammars). These levels constitute a taxonomy of theories (a grammar of a natural language being an example of such a theory) according to validation.
The formalism of context-free grammars was developed in the mid-1950s by Noam Chomsky, [3] and also their classification as a special type of formal grammar (which he called phrase-structure grammars). [4] Some authors, however, reserve the term for more restricted grammars in the Chomsky hierarchy: context-sensitive grammars or context-free ...
The term phrase structure grammar was originally introduced by Noam Chomsky as the term for grammar studied previously by Emil Post and Axel Thue (Post canonical systems).Some authors, however, reserve the term for more restricted grammars in the Chomsky hierarchy: context-sensitive grammars or context-free grammars.
Noam Chomsky's wife, Valeria Wasserman Chomsky, says reports Tuesday that the famed linguist and activist had died are untrue. Noam Chomsky, 95, had been hospitalized in Brazil while recovering ...
Thus, CSGs are positioned between context-free and unrestricted grammars in the Chomsky hierarchy. [ 1 ] A formal language that can be described by a context-sensitive grammar, or, equivalently, by a noncontracting grammar or a linear bounded automaton , is called a context-sensitive language .