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

paul c wrote:

> ... so I wonder
> what happens with "delete" to JOIN (which I believe is the operation
> that many people find controversial)?
> ...

Just as they find "insert" to UNION. The main argument seems to be that the operation is not deterministic when trying to decide on a base table by base table basis what to change, ie., there are three combinations of base values that could produce the same tuple in a view. McGoveran seemed to be saying that this argument is the wrong one, doesn't take in all available information because it manipulates extensions without concern as to the implications of the predicates and values involved before the insert or delete is tried.

It just seemed to me that if one started with the algebra and could somehow gauge all possible expressions as to what their resulting relations would be, one might find that McGoveran is right and if not, show that the problem is more complicated than he suggested. It also seemed to me that for such an exercise, if one had the right mental machinery, one could ignore the practical restrictions that are usually followed, such as common headings for union and run-time exceptions that some think will confuse dumb users. Received on Tue Dec 09 2008 - 00:16:23 CET