Generalizations
From: shane <shane_at_weasel.is-a-geek.net>
Date: Sun, 23 Mar 2008 16:13:47 +1300
Message-ID: <fs4hrj$7tc$1_at_lust.ihug.co.nz>
I hope it is ok to ask this here.
Im having trouble with ERD's.
I have been given a definition on which to draw an ERD. I did so, and began transforming the entities and relationships to relations using the following steps
Date: Sun, 23 Mar 2008 16:13:47 +1300
Message-ID: <fs4hrj$7tc$1_at_lust.ihug.co.nz>
I hope it is ok to ask this here.
Im having trouble with ERD's.
I have been given a definition on which to draw an ERD. I did so, and began transforming the entities and relationships to relations using the following steps
Step 1) Transform entities Step 2) Transform weak entities Step 3) Transform Relationships Step 4) Transform Generalizations Step 5) Simplify.
When I came upon step 4 I realised I had two opportunities to generalize. A
Doctor and a Patient (Both with SSN as their primary keys) could both be
specializations of a 'People' entity.
Could someone put me onto the right track?
TIA
Likewise Pharmacy and Pharmaceutical company are both specializations of
a 'company' entity.
I dont understand why we have the generalizations. It seems to me that we are
just creating a relation for the sake of it.
-- Hardware n: Parts of the computer you can kickReceived on Sun Mar 23 2008 - 04:13:47 CET