Difference between revisions of "Backus-Naur form"
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In the example shown above, <code><symbol></code> denotes a key, and the <code>__expression__</code> denotes a value. | In the example shown above, <code><symbol></code> denotes a key, and the <code>__expression__</code> denotes a value. | ||
* < | * <code><symbol></code>is a ''nonterminal'' (variable) and the <code>__expression__</code> consists of one or more sequences of either terminal or nonterminal symbols; | ||
* <code>=::=</code> means that the symbol on the left must be replaced with the expression on the right. | * <code>=::=</code> means that the symbol on the left must be replaced with the expression on the right. | ||
* more sequences | * more sequences of symbols are separated by the vertical bar "|", indicating an alternation choice, the whole being a possible substitution for the symbol on the left. | ||
Symbols that never appear on a left side are '' | Symbols that never appear on a left side are ''terminals''. On the other hand, symbols that appear on a left side are ''non-terminals'' and are always enclosed between the pair <code><></code>. | ||
Revision as of 11:58, 13 May 2022
Backus-Naur Form(Q211577), often abbreviated as BNF, is one of the two main notation techniques for context-free grammars in computer science.
BNF is a formal language that can be denoted in a collection of key-value pairs. For instance:
<symbol> ::= __expression__
In the example shown above, <symbol> denotes a key, and the __expression__ denotes a value.
<symbol>is a nonterminal (variable) and the__expression__consists of one or more sequences of either terminal or nonterminal symbols;=::=means that the symbol on the left must be replaced with the expression on the right.- more sequences of symbols are separated by the vertical bar "|", indicating an alternation choice, the whole being a possible substitution for the symbol on the left.
Symbols that never appear on a left side are terminals. On the other hand, symbols that appear on a left side are non-terminals and are always enclosed between the pair <>.