Re: constraints in algebra instead of calculus

From: paul c <toledobythesea_at_oohay.ac>
Date: Thu, 24 May 2007 00:33:23 GMT
Message-ID: <n355i.213914$6m4.168442@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).
>>
>>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 Wed May 23 2007 - 19:33:23 CDT