Re: primary key as subtype discriminator
Date: Thu, 4 Sep 2008 06:12:21 -0700 (PDT)
Message-ID: <7c5295f6-5fa3-4292-a082-2195c64772f9_at_v16g2000prc.googlegroups.com>
On Sep 3, 2:37 am, jefftyzzer <jefftyz..._at_sbcglobal.net> wrote:
> I think that's a bad idea. I know this may sound a bit shop-worn, but
Hi Jeff, thanks for your answer. I think that's a bad idea too, but
for different reasons. In my opinion the compound PK in the subtypes
becomes "redundant". You always know the value of part of the PK given
a subtype. I see this like a normalization error.
> all subtypes should be mutually exclusive and exhaustive. Further,
You can use a role entity to relax the mutual exclusivity requirement.
> they should each describe a semantically unique "kind of" the
> vs. smart key vs. surrogate key holy war. Besides, if the PK is, say,
> supertype, with each subtype described by attributes unique to it.
> a 4-byte unsigned integer, are you saying you'd have (in order to
> satisfy the "exhaustive" property) 4,294,967,296 subtypes?
What if, for instance, PK BETWEEN 1 AND 5? You are considering the whole 4-byte unsigned integer domain without constraints. Moreover I could use a natural key as category discriminator. Received on Thu Sep 04 2008 - 15:12:21 CEST