Re: constraints in algebra instead of calculus

"paul c" <toledobythesea_at_oohay.ac> wrote in message news:n355i.213914$6m4.168442_at_pd7urf1no...
> 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).
>>>

What if (A JOIN B){A} != A?
Should the constraint C apply to A - (A JOIN B){A}?

>>>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.
>
> p
Received on Thu May 24 2007 - 05:33:58 CEST