Re: Universal Quantifier
Date: Sat, 27 Jan 2007 14:42:32 GMT
Message-ID: <sxJuh.822551$R63.227083_at_pd7urf1no>
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; > ...
p Received on Sat Jan 27 2007 - 15:42:32 CET