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

From: NENASHI, Tegiri <tnmail42_at_gmail.com>
Date: 7 Nov 2006 09:26:30 -0800
Message-ID: <1162920390.762696.131280@h48g2000cwc.googlegroups.com>

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.

To complete my response that I gave before. I did not see that the union view that you gave had a element that is not in the database. The union view is a coproduct in the category language. Generally, the coproduct is not updatable but if one injects an element that is not in the database like one of the legs of the coproduct, it will be updatable. The universal property of updatability that the functor F:Mon(V)==>Mon(E) must be left and right fibration is honored. The proof is easy. Like I recollect the SQL union is never updatable.

--
Tegi

>

> > > BTW, how is that lawsuit against the movie industry is going?
> > > http://groups.google.com/group/alt.video.dvd.tech/browse_frm/thread/ec185c0b13e02f7e/b5537612074bd38d?lnk=st&q=&rnum=2&hl=en#b5537612074bd38d
> >
> > It is some confusion.
>
> There is some confusion? Coincidence I'd say.
Received on Tue Nov 07 2006 - 11:26:30 CST

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