Re: constraints in algebra instead of calculus

Bob Badour wrote:
> 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 either. What I feel should be simple but which I can't always explain very simply is something that I think needs to be explained since there is so much mumbo-jumbo in this field, usually propagated by commercial interests. Whether he knows it or not, Brian S is playing the part of a spokesman for the technocrats. Perhaps instead of criticizing him, I should criticize the many readers, I think, of this group who read without thinking. Not to say that there is only one measure of thought, each of us can only do that as best we can. But when somebody varies or even twists the subject so frequently, it indicates to me that the effort is not entirely earnest.

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