Date: Sat, 05 Jan 2008 09:25:48 GMT
"Marshall" <marshall.spight_at_gmail.com> wrote in message
> On Jan 4, 8:49 pm, "Brian Selzer" <br..._at_selzer-software.com> wrote:
>> I'm not sure what you mean. Can you please elaborate on the distinction
>> between what it means for information to be missing at the conceptural
>> and the logical layer? As far as I'm concerned, if there is a difference
>> between what is the case and what is represented in the database, that
>> if there is information that could be represented in the database but
>> then that information is missing. If a model has no nulls but there is a
>> difference between what is the case and what is represented in the
>> then at least one relation must be subject to an open world
>> (if there's no row, then you don't know) instead of the closed world
>> interpretation (if there's no row, then it ain't so). That it can be
>> you don't know raises the spectre of 3VL, regardless of what layer you're
> The connection between the model and what is being modeled is
> only in our head. We can consider the model without considering
> what the state of the real world is. Indeed, we can have a model
> that doesn't even *have* a corresponding real-world aspect. So
> when we talk about "missing" information, that's an attribute of
> the map between the model and reality in our head. It's not
> an aspect or an attribute of the model. At all.
I disagree. With nulls there is an explicit indication that there is
information that exists but hasn't been supplied. It is not a matter of
interpretation. Without nulls, there is no explicit indication so it
becomes a matter of interpretation.
> zero or one members of set B, then we can do that in a system
> without nulls, or in a system with nulls. The question is, which
> way is better? The answer is, the way without nulls is better.
You're oversimplifying: If we have a set A, and for each member of A we /can/ have either zero or one members of set B, and for each case where we /can/ have one member of set B, a member /may/ have been specified. And yes, we can do that in a system without nulls, or in a system with nulls. Which way is better? I'm not ready to dismiss nulls simply because it is politic to do so.
Received on Sat Jan 05 2008 - 10:25:48 CET