Re: Why does 1:3 relationsihp require another table?
From: Louis Davidson (dr_dontspamme_sql_at_hotmail.com)
Date: 05/17/04
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Date: Sun, 16 May 2004 22:08:38 -0500
> >NULL? In fact, since no one has defined NULL, either, what property are
you
> >assuming of the symbol NULL that makes it always violate 1NF when it's
> >allowed? <<
> >
> >For any "symbol" to be a value that belongs to a domain, it must have the
> >same characteristics of the other values in that domain. And more
> >importantly the operations applicable to the values must the applicable
to
> >the "symbol" and that is where a symbol like NULL fails.
I disagree here completely. A null value has all of the same properties,
except for one thing. We don't know the properties. The values for the
properties are UNKNOWN. Does A = NULL. It might. It might not (and
probability speaking, it probably doesn't, unless we are dealing with a bit,
then it is 50-50.)
I think to say that the value is missing is very misleading, since the
English word for missing is vague. When someone leaves off their age on an
application it is missing, and when the insurance application asks me when
my last time of the month was, that value is missing (thank goodness :)
However, one of these is missing because of pride, so it is unknown. The
other value is not applicable, which is not unknown, so it should not be
represented by NULL. This is where subclassing and/or child tables (as in
the password) come in.
-- ---------------------------------------------------------------------------- Louis Davidson (drsql@hotmail.com) Compass Technology Management Pro SQL Server 2000 Database Design http://www.apress.com/book/bookDisplay.html?bID=266 Note: Please reply to the newsgroups only unless you are interested in consulting services. All other replies will be ignored :) "Steve Kass" <skass@drew.edu> wrote in message news:uSbTKq5OEHA.556@tk2msftngp13.phx.gbl...
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