Concepts inIndexed Grammars—An Extension of Context-Free Grammars
Indexed grammar
An indexed grammar is a formal grammar which describes indexed languages. They have three disjoint sets of symbols: the usual terminals and nonterminals, as well as index symbols, which appear only in intermediate derivation steps on a stack associated with the non-terminals of that step.
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Context-free grammar
In formal language theory, a context-free grammar (CFG) is a formal grammar in which every production rule is of the form V ¿ w where V is a single nonterminal symbol, and w is a string of terminals and/or nonterminals (w can be empty). The languages generated by context-free grammars are known as the context-free languages.
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Context-sensitive language
In theoretical computer science, a context-sensitive language is a formal language that can be defined by a context-sensitive grammar. That is one of the four types of grammars in the Chomsky hierarchy. Of the four, this is the least often used, in both theory and practice.
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Context-free language
In formal language theory, a context-free language is a language generated by some context-free grammar. The set of all context-free languages is identical to the set of languages accepted by pushdown automata.
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Regular language
In theoretical computer science and formal language theory, a regular language is a formal language that can be expressed using a regular expression. Note that the "regular expression" features provided with many programming languages are augmented with features that make them capable of recognizing languages that can not be expressed by the formal regular expressions (as formally defined below).
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Formal language
In mathematics, computer science, and linguistics, a formal language is a set of strings of symbols. The alphabet of a formal language is the set of symbols, letters, or tokens from which the strings of the language may be formed; frequently it is required to be finite. The strings formed from this alphabet are called words, and the words that belong to a particular formal language are sometimes called well-formed words or well-formed formulas.
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Grammar
In linguistics, grammar is the set of structural rules that govern the composition of clauses, phrases, and words in any given natural language. The term refers also to the study of such rules, and this field includes morphology, syntax, and phonology, often complemented by phonetics, semantics, and pragmatics. Linguists do not normally use the term to refer to orthographical rules, although usage books and style guides that call themselves grammars may also refer to spelling and punctuation.
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