In type 2 {Context-free Grammar}, rules start with variables and produce variable-and-constant series. Variables are start symbols for grammar subsets. Context-free grammars can accommodate parentheses. Rules do not depend on nearby symbols. Context-free grammars are equivalent to Recursive Transition Networks, which can refer to other transition networks.
parsing
Top-down parsers start with rules with variables and find places that match rules. Bottom-up parsers start with constants and make variables based on rules. Tree structures {parse tree, grammar} show how rules apply. Diagrams {sentence diagram, grammar} show sentence structure. Sentences can have more than one parse tree.
ambiguity
No universal algorithm can determine if context-free grammars are unambiguous or ambiguous or make ambiguous ones unambiguous.
number
Languages can have more than one context-free grammar.
normal form
Context-free grammars can have special forms {normal form, grammar}. Normal forms {Chomsky normal form} can have rules that make one variable into two variables or one constant, with no empty strings. Normal forms {Griebach normal form} can have rules that make one variable into two constants or one empty string.
Social Sciences>Linguistics>Grammar>Kinds>Quantitative>Formal
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Date Modified: 2022.0224