Re: Universal Quantifier

From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Sat, 27 Jan 2007 14:47:39 GMT
Message-ID: <fCJuh.5793$1x.100425@ursa-nb00s0.nbnet.nb.ca>

paul c wrote:

> Bob Badour wrote:
>

>> paul c wrote:
>>
>>> Marshall wrote:
>>>
>>>> On Jan 22, 11:02 am, "paul" <dm_ul..._at_yahoo.com> wrote:
>>>>
>>>>> Does someone know where I can learn more about Universal Quantifier
>>>>> (Predicate logica) in relation with Database design.
>>>>
>>>> Why not start here:
>>>>
>>>> http://en.wikipedia.org/wiki/Universal_quantification
>>>>
>>>> Always fun to spend an evening chasing Wikipedia links. At least
>>>> until you end up at an article about a metal band.
>>>>
>>>> Consider that database constraints can be expressed as quantified
>>>> logical formula. If table A has primary key p and table B has attribute
>>>> q which is a foreign key referencing A(p), we could express that as:
>>>>
>>>>   forall B(q). exists A(p). p=q;
>>>> ...
>>>
>>> What formula would express a primary key?
>>
>> Faking it heavily, I suggest something along the lines of:
>>
>> forall A1(p1,q1) in A(p,q). forall A2(p2,q2) in A(p,q).
>>   if p1 = p2 then q1 = q2;
>> ...

>
> Thanks. Is that equivalent to:
>
> forall A1(p1,q1) in A(p,q). forall A2(p2,q2) in A(p,q).
> not (p1 = p2) or (q1 = q2);
>
> or does the "if ... then ..." stand for something else?

Yes, it is equivalent. Thank you. Received on Sat Jan 27 2007 - 08:47:39 CST