Re: View Updates Problem Statement

"Bob Badour" <bbadour_at_golden.net> wrote in message news:O3b7b.733$QQ.69871762_at_mantis.golden.net...
> "Mikito Harakiri" <mikharakiri_at_ywho.com> wrote in message
> news:Yw97b.27$741.210_at_news.oracle.com...
> > 1. We need to consider more than one view in order to be able solve
> > ambiguous cases.
>
> That doesn't make any sense because the user did not mention any other
view.

That entirely depends upon view update context. Suppose we have "data integration" problem.

Database A has relations RA1, RA2, RA3, ... Database B has relations RB1, RB2, ...

Views V1, V2, V3, ... establish the mapping between the 2 databases:

V1*RA1 = RB1
V2*RA2 = RB2
...

Problem. Translate each update in database B into database A.

We, therefore, have at least one view update problem with many views.

Now let's change "relations in the database A" to "base relations", and "relations in the database B" into "views" (in the same database). That sounds like original view updates formulation.

What is wrong with user knowing the effect of update on a set of views V1, V2, ... ?

> > 3. Constraints are views that evaluate to constants. For example, if we
> > define
> >
> > view V3
> > select max(sal) from (
> > select sal from emp
> > union
> > select 1000 from DEE
> > )
> >
> > then constraint "each emp has salary no more than 1000" can
algebraically
> be
> > written as
> >
> > V3*x = 1000
> >
> > where "V3*x" means view V3 applied to a set of base relations x, and
> "1000"
> > means an output relation that has one tuple with a single value 1000.
>
> What set of relations are you talking about? V3 references emp and DEE. Or
> are you talking about the possible values of emp and DEE?

Date's DEE is a constant relation containing one tuple. I introduced it in order to transform inequality into equality. Emp is the only relation variable that is used in the V3. But it can be many. We can assume that a view input is the set of all base relations, while view output doesn't necessarily depend upon all of them. Received on Mon Sep 08 2003 - 20:58:31 CDT