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

On Dec 8, 4:13 pm, vadim..._at_gmail.com wrote:
> As for deletion here is my worksheet
....
> Now, we are proving the following decomposition
>
> (SP v D')^(S v D') = (SP ^ S) v D'.

This assertion is wrong. If D is the set of tuples that we delete from SP ^ S, then the condition is:

(SP ^ (D' v (SP ^ R00))) ^ (S ^ (D' v (S ^ R00))) = (SP ^ S) ^ D'

Informally, on the right side we have a relation which is the result of deleting D tuples from SP ^ S. On the left side is a relation that is a join of two base relations SP and S, each trimmed with some projection of D.

I fail to derive it with any assumptions, except the obvious, like demanding that D acted only on SP (or S). Therefore, there might be some truth to people questioning the validity of deletion from join view... Received on Thu Dec 11 2008 - 22:28:55 CET