Re: [Gnumed-devel] Re: [openhealth] Consolidation Proposal: ClearHealth, FreeMED and OpenEMR

[Horst Herb]

On Wed, 15 Jun 2005 17:11, Tim Cook wrote:
> > > 3) do you allow any nulls in your database?
> >
> > Yes, hopefully only where appropriate. Please do point out any
> > flaws you find.
>
> There are no appropriate places for NULLS in a "relational" data model.

Not in the "umpteenth" normal form. But nobody goes that far in practice, or 
am I wrong?

NULLs are very appropriate in places where clustering data into a not so 
highly normalized table and at the time of first data recording that data was 
not available yet.

Example: a person has one and only one date of birth, and this date of birth 
is unrelated to the "same" date of birth of any other primary key (person). 
It makes sense to store that attribute together with the personal identifier 
instead of in a separate table. But at the time I create a new "person" I 
might not be able to inquire the date of birth, so I leave it as "NULL".
 
Horst