Re: Why relational division is so uncommon?

Vadim Tropashko <vadimtro_invalid_at_yahoo.com> wrote in news:1177607284.813162.87940_at_t38g2000prd.googlegroups.com:

> This is an interesting observation as well. Consider a medical
> database schema:
>
> PatientSymptom (
> name string,
> symptom string
> )
>
> DeceaseSymptom (
> name string,
> symptom string
> )
>
> Would db designers pressed hard to avoid set joins and create a
> redundant relation

The db designers won't be hard pressed to avoid set containment joins at all because the above schema does't have any set valued attributes to join on -:)

What relation is redundant depends on your point of view. 'Symptom string' is an ugly hack to emulate relational division for the original table you've specified below. You surely do not claim that the symptom string is a set valued attribute, do you ? Medical db developers usually have to maintain both tables for obvious reasons.

>
> PatientDeceases (
> patient_name string,
> decease_name string,
> )
>
> ?
>
>
>
>
Received on Fri Apr 27 2007 - 00:22:45 CEST