Re: Object-oriented thinking in SQL context?

On Jun 19, 2:12 am, "Brian Selzer" <br..._at_selzer-software.com> wrote:
> "rpost" <rp..._at_pcwin518.campus.tue.nl> wrote in message
>
> news:h1eass$2imf$4_at_mud.stack.nl...
>
> > Brian Selzer wrote:
>
> > [...]
>
> >>[...]  The view update problem is the result of the ambiguity inherent
> >>in the relational expressions that define views.
>
> > Perhaps it helps to state the cause of the ambiguity: when an expression
> > defines a non-injective transformation, there is no (unique) inverse
> > transformation, hence the ambiguity.
>
> Yes, that's it.  Whenever the mapping between the base relation(s) and the
> derived relation is onto but not one-to-one, that is, a surjection that is
> not also an injection, there is no (unique) inverse transformation.
>
> > --
> > Reinier

I realise this, it is exactly because of this that I wanted to include the tuples of the base relation(s) as attributes of the tuples of the derived relation - to allow the user to modify the premises instead of the conclusion. On second thought, I suppose the user could just select those tuples directly from the base relation, if they needed them.

Nilone Received on Fri Jun 19 2009 - 02:25:34 CEST