Re: Basic question?What 's the key if there 's no FD(Functional Dependencies)?

Aloha Kakuikanu wrote:
> NENASHI, Tegiri wrote:
> > Aloha Kakuikanu wrote:
> > > NENASHI, Tegiri wrote:
> > > > Jan Hidders wrote:
> > > > > Do you know of any results that might be interesting for database
> > > > > theory and could not already be shown with good old set theory?
> > > >
> > > > The categorical sketches to use for universal view updatability:
> > > >
> > > > Michael Johnson and Robert Rosebrugh.
> > > > Universal view updatability
> > >
> > > They claim to solve view updatability?
> >
> > No they claim to find out the universal property when the view can be
> > updated. See the article.
> >
> > >
> > OK, I have a table RealPeople
> > > with one attribute Name and the view
> > >
> > > CDTPosters =
> > > RealPeople
> > > union
> > > {(name=TeGiriNeNashi)}
> > >
> > > and a constraint
> > >
> > > RealPeople
> > > intersect
> > > {(name=TeGiriNeNashi)}
> > > =
> > > {}
> > >
> > > Is the CDTPosters view updatable?
> > >
> >
> > In sketches the constraints are defined by diagram commutability. The
> > view is not updatable because the diagram does not commute.
>
> This conclusion is unsatisfactory. The view is updatable.

You are right. I did not look with attention at your sql. You are right, the diagram will commute because the supersketch does not change the base sketch.
>

--
Tegi