Re: Proposal: 6NF
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Thu, 05 Oct 2006 13:36:33 GMT
Message-ID: <BT7Vg.689$cz.9969_at_ursa-nb00s0.nbnet.nb.ca>
>
> I'd add that the same applies if we want the relational model to be
> closed under arbitrary unions. To me that seems somehow more elementary,
> and it also ties neatly with inheritance modelling: even if you
> represent entities of subtypes and supertypes by different relations,
> sometimes it's handier to work on their union.
Date: Thu, 05 Oct 2006 13:36:33 GMT
Message-ID: <BT7Vg.689$cz.9969_at_ursa-nb00s0.nbnet.nb.ca>
Sampo Syreeni wrote:
> On 2006-10-05, David Cressey wrote:
>
>> An outer join between two relational tables will, in general, produce >> a table with nullable columns.
>
> I'd add that the same applies if we want the relational model to be
> closed under arbitrary unions. To me that seems somehow more elementary,
> and it also ties neatly with inheritance modelling: even if you
> represent entities of subtypes and supertypes by different relations,
> sometimes it's handier to work on their union.
You are making a great blunder. Null is totally unecessary for handling specialization and generalization. Received on Thu Oct 05 2006 - 15:36:33 CEST