Re: constraints in algebra instead of calculus

From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Thu, 24 May 2007 00:17:50 -0300
Message-ID: <46550391$0$4021$9a566e8b@news.aliant.net>

paul c wrote:

> Brian Selzer wrote:
>

>> "paul c" <toledobythesea_at_oohay.ac> wrote in message
>>
>>>  ...
>>> If view V = A & B, surely constraint C on the view, giving V & C, 
>>> would be manipulated by an engine with the same effect as the 
>>> expression (A & C) & (B & C).
>>>
>>> I've never heard of anybody requiring expressions to result in BCNF 
>>> values, surely that would cripple an algebra.
>>
>> They don't.  Nor should they.  But an expression defining a view can 
>> involve anything, restriction, difference, aggregation, division.  How 
>> does a constraint on the view map to constraints on the base tables?

>
> I would think restriction and difference can be distributed naively as
> above. If nobody else here formulates the other two, I'll be getting
> around to it in the next few months for other reasons.

I don't know why you indulge him. Constraints are simply wffs. One can map a view constraint to the base relations by simple substitution. Received on Wed May 23 2007 - 22:17:50 CDT