Re: One to One relationships
Date: Thu, 24 Apr 2003 11:52:35 -0400
Message-ID: <UkUpa.617$dW4.122681483_at_mantis.golden.net>
"Jeffrey Bailey" <mrwizard1208_at_yahoo.com> wrote in message
news:vMSpa.254765$o8.4232841_at_twister.tampabay.rr.com...
> I use a one to one relationship to define sub-categories of items.
Whether
> or not this is correct, I don't konw. One of the best examples I can
think
> of comes from the aircraft parts industry. All parts have certain
> characteristics in common (partnumber, serialnumber, qty, etc.) only
certain
> parts have other characteristics (time limiters). I store all parts in
the
> inventory table, and life-limited parts join in a one to one relationship
to
> a life-limited parts table for the extra values that describe them.
>
> This arrangement works well in practice. I also prevents the inventory
table
> from having characteristics that would be null for most parts(indicating
> unknown) or have to have an entry indicating "not applicable".
Unless I am mistaken, you have described a "one to zero or one" relative cardinality and not a "one to one". They are entirely different beasts. Received on Thu Apr 24 2003 - 17:52:35 CEST