Backus-Naur Form (BNF) grammars are used as a tool for describing language and command syntax, for example:
select-statement : SELECT select-list FROM table-name [ restriction ] [ ordering ]
restriction : WHERE search-condition
ordering : ORDER BY sort-order
A BNF definition states that the named item given before the colon is written as described after the colon. For example, an ordering is written as ORDER BY followed by a sort-order (which may be defined elsewhere).
BNF expression |
What it means |
named-construction : expression |
Declares that a named-construction is written as expression. |
named-construction : expression1 expression2 |
Declares that a named-construction is written as either expression1 or expression2. |
word |
The word word, written literally. |
exp1 exp2 |
exp1 followed by exp2. |
[exp] |
exp is optional. |
[ exp1 | exp2 ] |
Either exp1 or exp2 or nothing. |
<exp> |
exp is an entity or name that you specify. |
exp + |
expression, repeated one or more times. |
exp * |
expression, repeated zero, one or more times. |