6.12 BNF and EBNF Notations

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6.12 BNF and EBNF Notations


Meta-symbols of BNF

::=	stands for ‘is defined as’
\|	stands for ‘or’
category-names	non-terminal symbols

Extra meta-symbols of EBNF

[]	optional items
{}	repetative items

BNF is an acronym for (John) Backus (and Peter) Naur Form.
A restricted variant of DTD used to specify the syntax rules of a language.
BNF is for the grammar of a context-free language.
Extended BNF (EBNF) adds the regular expression notation of regular languages (to allow more concise specifications).
EBNF is an ISO-14977 standard

real	::=	(integer \| decimal)? ’E’ integer
decimal	::=	integer ’.’ integer \| integer ’.’ \| ’.’ integer
integer	::=	digit+
digit	::=	‘0’ \| ‘1’ \| ‘2’ \| ‘3’ \| ‘4’ \| ‘5’ \| ‘6’ \| ‘7’ \| ‘8’ \| ‘9’

Derivation:

real		decimal ‘E’ integer
		integer ‘.’ integer ‘E’ integer
		digit+ ‘.’ digit+ ‘E’ digit+
		‘12.3E45’

Derivation tree:

               real
                |
        +-------+---+----+
        |           |    |
     decimal        |    |
        |           |    |
   +----+-----+     |    |
   |    |     |     |    |
integer |  integer  | integer
   |    |     |     |    |
digit+ |   digit+  |  digit+
   |    |     |     |    |
+-+-+  |     |     |  +-+-+
|   |  |     |     |  |   |
1   2  .     3     E  4   5

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