Re: Date and McGoveran comments on view updating 'problem'

On Dec 11, 2:03 pm, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
> A more important question is: How would one write a constraint that
> deletes from SP ^ S affect SP but not S?

(S ^ D) v R00 = R00

With this constraint the view update proves easily.

(z ^ x) v R00 = R00 &
(x ^ y) ^ R00 = z ^ R00 &
(z ^ (x ^ y)) = z

> I assume the constraint would say that combining D with SP would yield
> an empty relation of some sort while combining D with S would yield a
> non-empty relation. I think these equations will be necessary to yield a
> determinate result.

If you are implying that presence of D in the constraint is somewhat unfortunate, then I agree. Received on Thu Dec 11 2008 - 23:36:01 CET