View source for Backus-Naur form

{{WikiEntry|key=Backus-Naur Form|qCode=211577}}, 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 pair]]s. For instance:
<syntaxhighlight lang=BNF>
  <symbol> ::= __expression__
</syntaxhighlight>
In the example shown above, <code><symbol></code> denotes a [[key-value pair|key]], and <code>__expression__</code> denotes a [[key-value pair|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.
* 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 <code><></code>.


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=References=
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==Related Pages==
[[Category:Meta Language]] 
[[Category:Universal Data Abstraction]] 
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