Re: View Updates Problem Statement

"Mikito Harakiri" <mikharakiri_at_ywho.com> wrote in message news:Yw97b.27$741.210_at_news.oracle.com...
> > "Bob Badour" <bbadour_at_golden.net> wrote in message
> > news:Vd97b.717$zB.69216404_at_mantis.golden.net...
> > > Suppose we extend the syntax for view definition to allow systematic
> > default
> > > values:
> > >
> > > view A as
> > > select a from X
> > > default X set b = 0 on insert to A
>
> Here is alternative suggestion:
>
> Given a set of views
>
> V1, V2, ... VN
>
> and a set of insert/delete operations upon those views, for example
>
> insert ('John', 20) into V1
> delete from V2 where name = 'Mary'
> ...
>
> translate those view updates into the base relations.
>
> Comments.
> 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.

> 2. It is not clear if artificially combining views like in the example of
> union&symmetric difference is a good idea.

I think it is pretty clearly a bad idea.

> 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? Received on Tue Sep 09 2003 - 03:15:26 CEST