# Re: Counting propositions

Date: Thu, 17 Jun 2004 09:46:52 +0300

Message-ID: <40d13d66_at_post.usenet.com>

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"Paul" <paul_at_test.com> wrote in message
news:O74Ac.15992$NK4.2654639_at_stones.force9.net...

*> x wrote:
**> > If tuples in a relational relation(ship) (or relvar) are propositions,
*

what

*> > is the meaning of :
**> >
**> > select count(distinct *) as nr
**> > from <relvar>
**>
*

> A relation corresponds to a set of propositions that all follow the same

*> predicate "template". So your predicate might be:
**>
**> p(x,y,z)
**>
**> where x,y,z are "variables" that range over values in domain sets X,Y,Z
**> say. But only some values of x,y,z will be true.
**> There will be |X|.|Y|.|Z| possible ways of substituting values in the
**> predicate (where |X| is the number of elements in the set X).
*

> The closed world assumption says that everything not in the database is

*> false. And the "SELECT COUNT(*)" query is saying how many values of
**> (x,y,z) there are for which p(x,y,z) is true.
*

Best answer so far.

So we aren't counting the propositions, we are counting the (x,y,z) values.
Why is this useful ?

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