Re: Devising a grammar for boolean queries

Bemmu Sepponen at lomise@uta.fi wrote on 10/31/00 12:37 PM:


> I assume the precedence of "and" and "or" is the same (true?).


Depends on your system. Most programming languages actually give
AND a higher precedence than OR. (well, most programming languages
I know, anyway).




> query -> phrase | phrase operator query
> operator -> and | or
> phrase -> word | word phrase
>
> Am I even close? How about the parentheses?


Almost any compiler text, which you should definitely take a look at,
will discuss expression grammars. For something as simple as the above
(ignoring parentheses) you can can use a regular expression:


query: phrase ( operator phrase )*


Of course, if you want precedence *and* nested expressions (parentheses)
then you will need a grammar. The exact grammar you should use depends
on how (and if) you intend to implement the grammar. For that, see
a compiler text.
Randy Hyde

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