Re: Principal of view equality?
Date: Mon, 9 Jun 2008 23:40:45 -0400
"Evan Keel" <evankeel_at_sbcglobal.net> wrote in message
> "Bob Badour" <bbadour_at_pei.sympatico.ca> wrote in message
>> 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. Received on Mon Jun 09 2008 - 22:40:45 CDT