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

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?

I don't think updatability is a uniform quality. Some updates may succeed, and some not. For example, there is a row in CDTPosters like this: (name=TeGiriNeNashi) and you certainly won't be able to delete this row under any circumstances. However you could perhaps delete any other row and not have the same problem.

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.

Marshall Received on Sat Nov 04 2006 - 03:22:47 CET