Encyclopedia > Extended Backus-Naur form

  Article Content

Extended Backus-Naur form

The Extended Backus-Naur form (EBNF) is any variation on the basic Backus-Naur form (BNF) metasyntax[?] notation with (some of) the following additional constructs:
  • square brackets "[..]" surrounding optional items,
  • suffix "*" for Kleene closure (a sequence of zero or more of an item), suffix "+" for one or more of an item, curly brackets enclosing a list of alternatives,
  • super/subscripts indicating between n and m occurrences.

When Niklaus Wirth was developing Pascal, he simplified Backus-Naur Form to create EBNF.

All these constructs can be expressed in plain BNF using extra productions and have been added for readability and succinctness.

There is an International standard (ISO 14977) that defines an EBNF. A draft is freely available from http://www.cl.cam.ac.uk/~mgk25/iso-ebnf. This draft document has some mistakes in it. Throughout the text, as well as in the comments of the examples, `meta-identifiers' are `written as one or more words joined together by hyphens' (as stated in section 4). On the other hand, all examples (except the comments) use spaces to separate several words.

The W3C used a different EBNF (http://www.w3c.org/TR/REC-xml#sec-notation) to specify the XML syntax.


This article (or an earlier version of it) contains material from FOLDOC, used with permission.



All Wikipedia text is available under the terms of the GNU Free Documentation License

 
  Search Encyclopedia

Search over one million articles, find something about almost anything!
 
 
  
  Featured Article
North Haven, New York

... of it is land and none of the area is covered with water. Demographics As of the census of 2000, there are 743 people, 337 households, and 209 families residing in ...

 
 
 
This page was created in 34.6 ms