Re: Inheritance Algebra

On Wed, Dec 21, 2005 at 01:52:34PM +0100, Martijn van Oosterhout wrote:

> On Sun, Dec 04, 2005 at 10:59:10PM -0700, Trent Shipley wrote:
> > Relational Constraint Inheritance Algebra
> > With regard to class and attribute uniqueness
>
> It's taken a while to digest this and sorry for the delay. While I find
> the ideas intreguing there is a little voice in the back of my head
> asking: practical applications?
I would assume quite a few people would use table
inheritance in a simple way were it available in a more
convenient fashion: to transport fields, primary and foreign
keys to child tables.

In GNUmed (a medical practice application)
http://salaam.homeunix.com/twiki/bin/view/Gnumed/WebHome
we use inheritance to make tables inherit

a) audit fields
b) common clinical fields such as a pointer to the patient

We overcome the primary/foreign key problem by a) letting
child tables have their own primary key which is quite
useful anyways and b) re-declaring foreign keys on child
tables.

While using inheritance isn't strictly necessary it is quite
convenient and makes the schema more intuitive.

There's also one major gain: since all clinical child tables
store their unstructured narrative in a field provided by
the clin_root_item parent table doing a search across the
entire narrative of the medical record is a simple query
against one table.

http://cvs.savannah.gnu.org/viewcvs/gnumed/gnumed/server/sql/?root=gnumed

(see gmAudit.sql and gmclinical.sql)

> The only situation I've come across inheitence being truly useful would
> be where you have several different "services" which are associated
> with a customer but each require different services.
Yes, this is similar to what we do.

Karsten
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