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Applying the rules recursively to a source string of symbols will usually terminate in a final output string consisting only of terminal symbols. Consider a grammar defined by two rules. In this grammar, the symbol Б is a terminal symbol and Ψ is both a non-terminal symbol and the start symbol. The production rules for creating strings are as ...
where A, B, S ∈ N are non-terminal symbols, a ∈ Σ is a terminal symbol, and ε denotes the empty string, i.e. the string of length 0. S is called the start symbol. In a left-regular grammar, (also called left-linear grammar), all rules obey the forms A → a; A → Ba; A → ε
A nonterminal symbol is called productive, or generating, if there is a derivation for some string of terminal symbols. X {\displaystyle X} is called reachable if there is a derivation S ⇒ ∗ α X β {\displaystyle S{\stackrel {*}{\Rightarrow }}\alpha X\beta } for some strings α , β {\displaystyle \alpha ,\beta } of nonterminal and ...
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Unlike a semi-Thue system, which is wholly defined by these rules, a grammar further distinguishes between two kinds of symbols: nonterminal and terminal symbols; each left-hand side must contain at least one nonterminal symbol. It also distinguishes a special nonterminal symbol, called the start symbol.
Terminal punctuation refers to the punctuation marks used to identify the end of a portion of text. Terminal punctuation marks are also referred to as end marks [1] and stops. [2] In languages using the ISO basic Latin alphabet, terminal punctuation marks are defined as the period, the question mark, and the exclamation mark.
where A, B, and C are nonterminal symbols, the letter a is a terminal symbol (a symbol that represents a constant value), S is the start symbol, and ε denotes the empty string. Also, neither B nor C may be the start symbol, and the third production rule can only appear if ε is in L(G), the language produced by the context-free grammar G.
An EBNF consists of terminal symbols and non-terminal production rules which are the restrictions governing how terminal symbols can be combined into a valid sequence. Examples of terminal symbols include alphanumeric characters, punctuation marks, and whitespace characters.