Re: teaching relational basics to people, questions

From: Casey Hawthorne <>
Date: Tue, 17 Nov 2009 23:37:25 -0800
Message-ID: <>

Somebody once called me pretentious.

I replied, "Moi?"

On Mon, 16 Nov 2009 11:42:21 -0800 (PST), Sampo Syreeni <> wrote:

>Right now it is to be expected that I will be spreading the good
>relational word among my peers, in the near future. That is an
>opportunity one doesn't want to fuck up; many enough have gone down
>that road already. So I've been going over, and over, and over the
>basics. Don't want them to be able to catch me off guard with the
>minutiae, after all...
>So now I bump into my first real surprise, and the chills immediately
>go down my spine. That's Date et al.'s answer regarding the
>implications between 6NF and DK/NF, at
>. In there they flat out state that DK/NF doesn't imply 6NF.
>So, my first question is, can this really be true? I mean, this seems
>highly suspect to me: since 6NF is a normal form like any other and is
>as such defined by the constraints it upholds by design, and on the
>other hand DK/NF is by definition a normal form where any constraint
>whatsoever follows from the domain and key ones, shouldn't it be self-
>evident that DK/NF logically implies 6NF, and in fact any other form?
>No matter the fact that there might well be databases which could be
>put into 6NF which cannot attain DK/NF? I think at the very least said
>implication should follow at the price of making it a vacuous truth
>(i.e. all (non-trivial?) 6NF databases could be such that they cannot
>be put into DK/NF)?
>In particular I suspect that the seeming lack of implication follows
>from not treating the time dimension(s) on an equal footing with the
>rest of the attributes in a relation. That, then, would at least to me
>seem like a rather grave violation of the information principle.
>The second point ain't as much a rebuke as a retort: I wonder whether
>Date and Darwen chose their model of time -- which 6NF is defined on
>top of -- based on convenience and familiarity, instead of some deeper
>theoretical reasoning. To me the idea that time in a relational
>database should be treated as a discrete, countably infinite set of
>disjoint moments at a preset temporal granularity seems just
>unnatural, and unnecessarily limiting.
>To me it would seem much more natural to model time as a full
>continuum of precise moments in time, and to constrain such real life
>models using a finite (but otherwise unlimited cardinality) set of
>FOPL constraints, relying on the full linear order on top of the
>reals, on top. I.e. to model time using CW-complexes over the real
>line (i.e. finite unions of open, closed and semi-closed intervals of
>reals), in a fully discrete but also fully variable precision
>Model-wise, 6NF as D&D define it immediately generalizes to this --
>all that needs to be changed is to quantify every defining formula
>over the corresponding nondenumerable set -- yet the possibility of
>rigorously modelling the interaction between open and closed intervals
>as well is a considerable plus when dealing with general intersection
>queries. I also consider the the fact that imputing any kind of chosen-
>ahead granularity parameter into the basic model suddenly becomes
>unnecessary a huge plus. So, do you think this sort of approach is
>Finally, I of course have the firm intention of covering the
>essentials, including the basics of dependency and normalization
>theory at least upto 6NF and DK/NF. If my audience proves to be game,
>I'd also like to mention in passing some of the lesser known, more
>esoteric, and less fully researched topics in dependency theory like
>(E)(B)MVD's (cf. e.g.
>), just to make sure people don't accidentally think they've mastered
>the subject after what is a mere, hurried, introduction. I'd hope to
>pique some genuine interest in the relational way of thought, among
>people who perhaps haven't been exposed to the mindset, eventhough
>otherwise more than capable in modelling data. If you could suggest
>other ways to accomplish the feat, I would greatly appreciate a hint.

Received on Wed Nov 18 2009 - 08:37:25 CET

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