Re: relative complement?

On 18 mrt, 22:44, paul c <anonym..._at_not-for-mail.invalid> wrote:

> But every time I've tried to imagine what the database
> looks like that they suggest has views that are ambiguous where certain
> assertions are concerned, I see no ambiguity, just arbitrary biases.

There might be a difference between what _YOU_ see when you look at that database, and what the _DBMS_ sees when it "looks" at that database.

_YOU_ are likely to look at that database with at least a background awareness of what the _EXTERNAL_ predicates of the relvars are, plus probably also with some awareness of what the "external predicates" of the constraints on that database are. The _DBMS_ cannot do such a thing. All the DBMS can do is to observe that "there are n (say, 3) base relvars involved in this view, and there are m (say, 17) database constraints involved with any of those n relvars, and the nature of those database constraints can be really just anything". I have come to be more and more convinced of the notion that getting a DBMS to provide sensible support for view updating will require that DBMS to "understand" constraints in exactly the same way as a human "understands" them. And that's a tall order.

And if you could explain to me _what it is that you see_ (I mean the "external predicate things" that you see), when you look at a database, in such a way that you can define it (what you see) in _formal, mathematical, algebraic, calculus_ terms, then I would start implementing and become a wealthy man in no time at all (after my implementation work is done, of course). Received on Sat Mar 19 2011 - 01:00:27 CET