Re: foreign key constraint versus referential integrity constraint

On 25 oct, 04:56, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
> paul c wrote:
> > Bob Badour wrote:
> > ...
>
> >> You asked about semantic joinability. Semantically, the join works if
> >> like-named attributes have an equality comparison defined and not if
> >> they don't.
> >> ...
>
> > In RT, how could they not define equality?
>
> What reason would one have to define an equality comparison to compare
> employee ids with department ids or with names? Or charge with current
> or potential? Or age with price?
Hi paul,

A valid set of questions (pun intended). My conclusion were that Codd was focused onto defining a side of the relational model that would be part of information system as opposed as being a part of mathematics since relational domain analysis is more loosely coupled with set theory than relational general model. While relational domain analysis is not mandatory in the context of the general relational model, it is mandatory in the context of implementation of RM. It even makes header based definitions somehow moot...IMHO...

Regards... Received on Sun Oct 25 2009 - 08:24:01 CET