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

vadimtro_at_gmail.com wrote:

> 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?

>>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.

I was not trying to imply that. I tend to agree it is a little unfortunate, but better to have some way to express it than to have no way at all.

I long ago concluded the 'problematic' view updates were all just cases of insufficient information yielding indeterminate results. Nobody seems to worry too much that one cannot solve for three variables using two linear equations. I don't see why anyone should fret too much over deletes of joins as long as the symbolic language has some way to disambiguate. Received on Fri Dec 12 2008 - 00:06:27 CET