Difference between revisions of "Backus-Naur form"
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* <[[symbol]]>is a ''[[nonterminal]]'' (variable) and the [[expression (mathematics)|__expression__]] consists of one or more sequences of either terminal or nonterminal symbols; | * <[[symbol]]>is a ''[[nonterminal]]'' (variable) and the [[expression (mathematics)|__expression__]] 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. | ||
* more sequences [of symbols] are separated by the [[vertical bar]] "|", indicating a [[alternation (formal language theory)|choice]], the whole being a possible substitution for the symbol on the left. | * more sequences [of symbols] are separated by the [[vertical bar]] "|", indicating a [[alternation (formal language theory)|choice]], the whole being a possible substitution for the symbol on the left. | ||
Revision as of 11:50, 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__
- <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 a 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 <>.
Key-value Pair Interpretation
In the example shown above, <symbol> denotes a key, and the __expression__ denotes a value.