Re: Modelling Disjoint Subtypes

Joe Thurbon <usenet_at_thurbon.com> wrote in news:5NjMh.135$M.102_at_newsserver. bigpond.net.au:

> I have (another) question about examples in Pascal's "Practical Issues
> in Database Management" book. This time it is about modelling disjoint
> entity subtypes.

Could anyone please provide a meaningful relational design example where disjoint entity subtype/supertype hierarchy would truly be beneficial ? I am aware of Pascal's example but do not find it convincing.

In other words, under what circumstances, other than an attempt to emulate object oriented viewpoint, "R <x, y>; R1 <super R, z>; R2 <super R, w>" is 'better' than just "R1<x,y,z>, R2<x,y,w>" ? What is achieved by such decomposition ? Clearly, there is no data redundancy because R1 and R2 are disjoint ! Received on Sat Mar 24 2007 - 18:04:53 CET