Re: Principal of view equality?
Date: Tue, 10 Jun 2008 09:49:55 -0400
Message-ID: <jEv3k.10255$co7.4524_at_nlpi066.nbdc.sbc.com>
"Brian Selzer" <brian_at_selzer-software.com> wrote in message
news:2Jm3k.926$LG4.296_at_nlpi065.nbdc.sbc.com...
>
> "Evan Keel" <evankeel_at_sbcglobal.net> wrote in message
> news:xge3k.7324$mh5.1673_at_nlpi067.nbdc.sbc.com...
> >
> > "Bob Badour" <bbadour_at_pei.sympatico.ca> wrote in message
> > news:4846bc21$0$4072$9a566e8b_at_news.aliant.net...
> >> paul c wrote:
> >>
> >> > I was just looking at Codd's RM 2 book again (the rather short
chapter
> >> > on views from acm.org) and it seemed to me that what he wrote took it
> >> > as
> >> > essential that a view must always equal the expression that defines
the
> >> > view. If so, does this in effect constitute a kind of indirect
> >> > constraint on any base relations involved?
> >>
> >> No. It does, however, specify constraints on the value of the view.
> >> Tuples can exist in the base relations that have no effect on the value
> >> of the view.
> >
> > I thought that "base relations" were also views. What am I missing?
> >
>
> A base relation is not a derived relation.
>
Yes, it is.
Evan Received on Tue Jun 10 2008 - 15:49:55 CEST