Re: ER diagram question
Date: Tue, 20 Jan 2004 14:00:37 -0000
Message-ID: <100qd45eaji1te3_at_corp.supernews.com>
jonck_at_vanderkogel.net (Jonck van der Kogel) wrote:
>> Can a Customer have a Communication independent of a Project?
>
>Uuhhhmmm.... good question :-) My original plans were that a Customer
>could only have a Communication coupled to a Project, but now that you
>ask, I think that it would be much better style if a Customer could
>have a Communication independent of a Project.
>But this makes it even more difficult! Do you see a solution?
>Your help is truly much appreciated, Jonck
It's only a better style if it's correct. Now look at a Project Communication
and a Customer Communication to see if there are any differences in attributes.
One possible solution is to create a super/sub type entity on the Communication
entity. One subtype called Customer Communication would have a relationship
to Customer, and the other subtype, Project Communication would have a relationship
to Project.
Received on Tue Jan 20 2004 - 15:00:37 CET