Backus Normal Form

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What Does Backus Normal Form Mean?

Backus Normal Form (BNF) is a metasyntactic notation procedure used to specify the syntax of computer programming languages, command/instruction sets, document formatting and communication protocols. BNF is applied when language descriptions are required.

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BNF is also known as Backus-Naur form.

Techopedia Explains Backus Normal Form

A BNF specification is a derivation rule set that is usually written as follows:

  • The <symbol>::_expression_where <symbol> is a non terminal
  • The _expression_consists of one or more symbol sequences.
  • A vertical bar (|) delineates other sequence options.
  • Symbols not appearing on the left side are terminals.
  • Symbols appearing on the left side are located within the symbol-expression pair and are non-terminals.
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Margaret Rouse
Technology Expert
Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.