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

Marshall wrote:
> On Nov 3, 4:57 pm, "Aloha Kakuikanu" <aloha.kakuik..._at_yahoo.com> 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? 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?

>

This is not much different from attempting to delete notexisting row.

delete from CDTPosters where name = 'AGuyFromAlphaCentauri'

fails

delete from CDTPosters where name = 'TeGiriNeNashi'

also fails

Although you may argue that updates succeeds in the first case with 0 record updated, while the whole transaction fails in the second case.

> It seems to me that whether a given update will succeed or not
> will not necessarily be able to be determined statically, but
> rather will depend on the current value of the variables involved.
> (And also the constraints of course.) So it's not clear to me
> what it would mean to say a view is updatable, with no
> further qualifications. I suppose we could say that it means
> that there exists at least one update that will succeed,
> but that doesn't seem like what is usually meant by the term.

What is the usual meaning of the term? Received on Sat Nov 04 2006 - 03:54:45 CET