Re: Table design question

"D Guntermann" <guntermann_at_hotmail.com> wrote in message news:HsMHuG.EtL_at_news.boeing.com...
>
> "Bob Badour" <bbadour_at_golden.net> wrote in message
> news:iqmdnQhOysUkBYfdRVn-jg_at_golden.net...
> > "Mike Sherrill" <MSherrillnonono_at_compuserve.com> wrote in message
> > news:qimk1018kh3htkap6gkdif05j1q8705v6v_at_4ax.com...
> > > On 25 Jan 2004 03:39:33 -0800, andrewst_at_onetel.net.uk (Tony) wrote:
> > >
> > > >But it isn't a domain: the domain of user ID numbers would be
> > > >something like "any 6 digit number between 100000 and 999999" or "a
> > > >string of between 3 and 30 letters and numbers"; whereas this table
> > > >represents the list of users who actually exist,
> > >
> > > Try thinking about it this way . . .
> > >
> > > At the conceptual level, a domain is just a data type, and a type is,
> > > among other things, a set of all possible values. One way to handle a
> > > set of values is to store them in a table.
> >
> > It's the "among other things" that kills you. A variable is not a time
> > invariant set of values and their associated operations.
> >
> >
> I'm not sure I understand, Bob.
>
> A variable holds a single value drawn from some domain. By virtue of the
> fact that the domain has been defined at some point in time as a set of
all
> possible values with operators, it should be time-invariant as long as the
> type specification holds.

The domain is defined for all time even if not specifically or completely declared to a dbms at any particular time.

> Why wouldn't it be invariant?

The variable or the domain? The domain is time invariant. The variable is not. Nor does the variable declare any operations.

> Computing devices are constricted to rather finite sets of
representations,
> as is logic. Are you saying that this constraint actually does not exist?

Not at all. Received on Thu Feb 05 2004 - 23:32:28 CET