Re: We claim that delete anomality is due to table not being in 3NF, but...

From: paul c <toledobythesea_at_oohay.ac>
Date: Fri, 07 Nov 2008 01:48:50 GMT
Message-ID: <68NQk.960$A73.926_at_edtnps82>

Roy Hann wrote:
> Hugo Kornelis wrote:
>

>> You're reading way more into my example than I intended. The point I
>> tried to make is that functional dependencies are not determined by what
>> is or is not stored in the database, but by how entities and their
>> interactions in reality. The DB is a model of reality and changing the
>> model won't change reality.

>
> The DB is NOT a model of reality. It is a model of the testimony users
> give about the bit of reality that interests them. And for the purposes
> of understanding what the database needs to do, we don't even have to
> require that the testimony be correct or even given in good faith.
> (Which is just as well because we can't do that.)

I think I'm with you both. While I think that we are attempting to model reality by designing a db, in my mind's eye, I always qualify that by seeing the model as highly abstract, which is essential if the logical machine is to avoid ambiguity. I'd rather say that a db doesn't copy reality.

>
> So, bottom line, the content of a database is only very indirectly
> connected to the real world, and is always suspect.
>
> Furthermore, the only thing we can insist on being able to rely upon is
> that the derivations we get from the content of the database are
> correct derivations from that content. To be assured of that we need to
> model the form of the testimony with proper fidelity. And that is what
> decides the appropriate functional dependencies.
>
> It's just math, not metaphysics.
>

When it comes to the "db machine", which must insist on absolute precision, again, to avoid ambiguity, the formality of math does seem necessary. Received on Fri Nov 07 2008 - 02:48:50 CET