Re: Table design problem

"Mike Sherrill" <MSherrill_at_compuserve.com> wrote in message news:b20p9vosbe28mc6g7mb1sfid6g5u5jcudi_at_4ax.com...
> On Tue, 8 Apr 2003 15:07:24 +0000 (UTC), "Roy Hann"
> <rhann_at_globalnet.co.uk> wrote:
>
> >> >I think I want to create a couple of subtype entities in an SQL
database.
> >> >In this database customers may be either of two subtypes: Individuals
or
> >> >Corporations.
> >>
> >> If individuals and corporations are really subtypes, then you should
> >> be looking at the supertype.
> >>
> >> Let's say the supertype "Parties" consists of the subtypes
> >> "Individuals" and "Organizations". Since both individuals and
> >> organizations can be customers, you'd associate customers with the
> >> supertype "Parties".
> >
> >Possibly I am missing your point,
>
> The points are that
>
> a) "Individual" describes a kind of party.
> b) "Organization" describes a kind of party.
> c) "Customer" describes a relationship between two parties.
>
> Individuals and organizations (that is, parties) exist regardless of
> whether they're customers. So instead of thinking "customers may be
> either of two subtypes: Individuals or Corporations", think "parties
> may be either of two subtypes--individuals or organizations", and "any
> party may be a customer".

OK, I think I see what you are getting at here. I think you are suggesting that my model ought to allow me to record the existence of a party regardless of whether they place an order (making them a customer). If I am correct about this, then I think you really just object (perhaps properly) to my table name being "customer". I never said so originally, but my model always did permit what I called a customer without any corresponding order. Furthermore, there are no attributes in the join of the new customer table and the new party table that would not also exist in my old customer table, so a separate party table and customer table don't appear to add any value. Indeed it appears spurious.

Or do I continue to miss the point?

Roy Received on Thu Apr 17 2003 - 12:14:25 CEST