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2. Context-free grammar - Wikipedia

   en.wikipedia.org/wiki/Context-free_grammar

   In formal language theory, a context-free grammar ( CFG) is a formal grammar whose production rules can be applied to a nonterminal symbol regardless of its context. In particular, in a context-free grammar, each production rule is of the form. with a single nonterminal symbol, and a string of terminals and/or nonterminals ( can be empty).

3. Chomsky hierarchy - Wikipedia

   en.wikipedia.org/wiki/Chomsky_hierarchy

   The general idea of a hierarchy of grammars was first described by Noam Chomsky in "Three models for the description of language". [1] Marcel-Paul Schützenberger also played a role in the development of the theory of formal languages; the paper "The algebraic theory of context free languages" [2] describes the modern hierarchy, including context-free grammars.

4. Context-free language - Wikipedia

   en.wikipedia.org/wiki/Context-free_language

   An example context-free language is , the language of all non-empty even-length strings, the entire first halves of which are a 's, and the entire second halves of which are b 's. L is generated by the grammar . This language is not regular . It is accepted by the pushdown automaton where is defined as follows: [note 1]

5. Chomsky normal form - Wikipedia

   en.wikipedia.org/wiki/Chomsky_normal_form

   In formal language theory, a context-free grammar, G, is said to be in Chomsky normal form (first described by Noam Chomsky) [ 1] if all of its production rules are of the form: [ 2][ 3] A → BC, or. A → a, or. S → ε,

6. Context-sensitive grammar - Wikipedia

   en.wikipedia.org/wiki/Context-sensitive_grammar

   Context-sensitive grammar. A context-sensitive grammar ( CSG) is a formal grammar in which the left-hand sides and right-hand sides of any production rules may be surrounded by a context of terminal and nonterminal symbols. Context-sensitive grammars are more general than context-free grammars, in the sense that there are languages that can be ...

7. Parse tree - Wikipedia

   en.wikipedia.org/wiki/Parse_tree

   Parse tree to SAAB. A parse tree or parsing tree [1] or derivation tree or concrete syntax tree is an ordered, rooted tree that represents the syntactic structure of a string according to some context-free grammar. The term parse tree itself is used primarily in computational linguistics; in theoretical syntax, the term syntax tree is more common.

8. Terminal and nonterminal symbols - Wikipedia

   en.wikipedia.org/wiki/Terminal_and_nonterminal...

   In fact, the language defined by a grammar is precisely the set of terminal strings that can be so derived. Context-free grammars are those grammars in which the left-hand side of each production rule consists of only a single nonterminal symbol. This restriction is non-trivial; not all languages can be generated by context-free grammars.

9. Generalized context-free grammar - Wikipedia

   en.wikipedia.org/wiki/Generalized_context-free...

   Generalized context-free grammar (GCFG) is a grammar formalism that expands on context-free grammars by adding potentially non-context-free composition functions to rewrite rules. [1] Head grammar (and its weak equivalents) is an instance of such a GCFG which is known to be especially adept at handling a wide variety of non-CF properties of ...