Re: What to call this operator?

From: paul c <>
Date: Tue, 28 Jun 2005 22:07:32 GMT
Message-ID: <ESjwe.1820496$Xk.1729912_at_pd7tw3no>

paul c wrote:
> Mikito Harakiri wrote:

>> paul c wrote:
>>> ...
>>> the place of <OR> in the world puzzles me too.  for one thing it appears
>>> to me that it produces the same result of <AND> when there are no
>>> attributes in common, ie. cartesian product.  am i wrong?
>> If relations have disjoint headers, the result would be an infinite
>> relation, not the Cartesian product.

> i gather that you are saying that the definition means i must infer all
> possible tuples given whatever domains their attributes specify rather
> than all possible tuples based only on the contents of the origial
> relations.
> just to see if i've got this straight i wonder if you'd check this:
> if may leave infinity out of it and if i may assume a common finite
> domain with symbols for its values of 1 and 2 and if i may order the
> attributes just for this purpose and i have r1=<1> and r2 = <1> but no
> common attribute names (ie. disjoint headers) then r1 <or> r2 would be
> <1,1>,<1,2>,<2,1>, whereas the cartesian product would be <1,1>.
> ...

to put it another way, if the result of <or> happens to be <a,b> i can interpret the result as:

a is true and b is true
or (in the more common sense, not the D&D <or>) a is true and b is false
a is false and b is true

but not "a is false and b is false".

i think now that is the way i should have approached the definition in the first place as it reads more like the usual definition of logical 'or'.

still, i can't get it through my head why it is important to allow infinite domains. granted that results for finite domains could still be very large, but othertimes they could be very small!

is the reason, say for integers, simply that integers in math are considered infinite? if so, there's some historical evidence that limiting them won't cause problems for many applications.

or is the thinking that the number of times results using infinite domains are small is no fewer than if the domains were finite?

thanks again,
p Received on Wed Jun 29 2005 - 00:07:32 CEST

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