Nabil wrote:
> Jan Hidders wrote:
>> Nabil wrote:
>>> [...] There exist some cases where it is usefull to store even
>>> those FD's that do not hold. Ofcourse we save these as not
>>> holding and do not use them while normalizing. Does ne1 know when
>>> it is helpfull to store fd's that do not hold??
>>
>> Sure, but this sounds a bit like a home-work problem, so could you
>> tell a bit more about why you want to know this?
>
> I am working as a Research assistant in my university and i was asked
> to find out if there are such cases. I have searched on google but
> for no use. I have not found such a case. I personally think there is
> no use of storing fd's that do not hold. a functional dependency is
> defined as such that if it does not hold it has no meaning. will be
> waiting for ur reply. if there is such a case then let me know. will
> be waiting for ur reply.
If you mean by storing and FD "specify it as a constraint" then it is
not only not useful, but in fact counterproductive since it may keep you
from entering valid data. But if you mean by storing "keeping an SQL
query around that checks if it is satsified" then it is potentially very
useful because there are often many constraints that should hold, but in
reality don't, and such a query allows you to check this.
Received on Thu Jun 02 2005 - 11:05:30 CDT
