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In formal language theory, an alphabet, sometimes called a vocabulary, is a non-empty set of indivisible symbols/characters/glyphs, [1] typically thought of as representing letters, characters, digits, phonemes, or even words.
A formal language L over an alphabet Σ is a subset of Σ *, that is, a set of words over that alphabet. Sometimes the sets of words are grouped into expressions, whereas rules and constraints may be formulated for the creation of 'well-formed expressions'.
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.
A formal grammar describes which strings from an alphabet of a formal language are valid according to the language's syntax. A grammar does not describe the meaning of the strings or what can be done with them in whatever context—only their form. A formal grammar is defined as a set of production rules for such strings in a formal language.
In formal language theory, a context-free grammar ... The set of terminals is the alphabet of the language defined by the grammar G. R is a finite relation in ...
A formal grammar includes a start symbol, a designated member of the set of nonterminals from which all the strings in the language may be derived by successive applications of the production rules. In fact, the language defined by a grammar is precisely the set of terminal strings that can be so derived.
Abstract family of languages; Abstract rewriting system; Abstract semantic graph; Abstract syntax tree; Action algebra; Adaptive grammar; Affix grammar; Agent Communications Language; Algorithmic learning theory; Alphabet (formal languages) Ambiguous grammar; Antimatroid; Arden's rule; Attribute grammar; Augmented Backus–Naur form ...
The set of formal symbols in a formal language is referred to as an alphabet (hence each symbol may be referred to as a "letter") [1] [page needed] A formal symbol as used in first-order logic may be a variable (member from a universe of discourse), a constant, a function (mapping to another member of universe) or a predicate (mapping to T/F).