Re: Universal Quantifier

Bob Badour wrote:
> paul c wrote:
>

>> Bob Badour wrote:
>>
>>> ...
>>>
>>>> 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;
>>>
>>> where p is actually the set of attributes composing the key and q is 
>>> actually the set of dependent attributes.
>>>
>>> One also has to express irreducibility, though.
>>
>>
>> Regarding irreducibility, do we not express it by our choice of p1 and
>> p2?  Ie., what we express with a reducible p1 is extraneous?

I think I see what you mean, will try to write it for myself - it does seem nice and precise to be able to say what property the irreducible set is by saying that a "proper" superset of it is reducible, assuming that's what you mean. Also would feel nice somehow, at least to me, if we could express table_dee and dum that way too, just trying to dot some i's.

p Received on Sat Jan 27 2007 - 23:34:31 CET