Re: foreign key constraint versus referential integrity constraint

From: paul c <>
Date: Mon, 26 Oct 2009 09:25:10 GMT
Message-ID: <WVdFm.50297$PH1.13360_at_edtnps82>

Cimode wrote:
> On 25 oct, 04:56, Bob Badour <> 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...

Cimode, I tend to look at it the same way, at least the part about the information system motive, not sure about headers. If I recall it wasn't until his second paper that he introduced the pair of attribute and domain name, he was adjusting his theory to meet practice. Received on Mon Oct 26 2009 - 10:25:10 CET

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