Re: Data Display & Modeling

From: x <x-false_at_yahoo.com>
Date: Wed, 12 May 2004 18:06:51 +0300
Message-ID: <40a23cc2$1_at_post.usenet.com>


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"Eric Kaun" <ekaun_at_yahoo.com> wrote in message news:yeqoc.1165$qr1.246_at_newssvr32.news.prodigy.com...
> "Dawn M. Wolthuis" <dwolt_at_tincat-group.com> wrote in message
> news:c7ioke$n22$1_at_news.netins.net...
> > "Eric Kaun" <ekaun_at_yahoo.com> wrote in message
> > news:YzQmc.86$Qm5.68_at_newssvr32.news.prodigy.com...
> > > And I should add that Levene contributed to the "Nested Relational
Data
> > > Model", which I believe Date discusses in Intro-DB Systems as
> unnecessary,
> > > and proceeds to show why the basic relational model can tackle the
same
> > > problem domains without modification (and with additional benefits). I
> > can't
> > > remember the details - Dawn?
> >
> > Although Date talks about relation-valued attributes in Intro-DB, I
> haven't
> > found anything describing a nested relational model (but I've not read
all
> > the way through). Instead he adds in the GROUP and UNGROUP operators in
> D.
> > However, there are a couple of papers that you can pay for and download
> from
> > dbdebunk.com where Date discusses nested structures and asks questions
> about
> > MultiValue (PICK) systems and then by Pascal who gives reasons not to
use
> > relational-valued attributes even though they are not outside of the
scope
> > of relational theory (anymore).

>

> I have "What First Normal Form REALLY Means" here, and it's worth buying,
> even for MVers. Some salient quotes from it, chosen for shock value:
>

> "... the notion of atomicity has no absolute meaning..." [and of course,
> atomicity is central to defining 1NF]
> "... a set like {P2, P4, P5} is no more or less decomposable by the DBMS
> than a character string is."
> "... relations are always in 1NF!"
> "It's certainly true that RVAs [relation-valued attributes] can be useful
in
> reports."
> "Domains, and therefore attributes or columns, can contain anything (any
> values, that is)."
> "... hierarchic designs usually arise from a limited perspective on the
> overall problem..."
> "... the hierarchic representation isn't suitable for all of the kinds of
> processing that we might need to do on the data."
> "You can't tell whether a given table is in 1NF just by looking at it..."
> "Supporting RVAs involves little in the way of additional learning... if
we
> were to introduce, say, arrays 'on the inside', then users would
necessarily
> have to understand arrays..."
>

> Obviously you can abuse this notion, but I thought you might enjoy this
> paper. It's certainly interesting, and not what's often argued with regard
> to 1NF.
>
> > > Not evidence of anything, except perhaps willingness to invent
novelties
> > > rather than exploiting what's already available
> >
> > Of course, that is what Codd did.
>

> True, although in my opinion he sticks closely to a very applicable and
> implementable theory. Higher-order logics are very useful, but first we
> should get our money's worth from first-order, which has a few miles left
in
> it, right? Relational is a fairly direct application of predicate logic
> without frills and extras, in my opinion, but I could of course be biased.
> Perhaps the DBs he helped replace lacked theory, and thus any theory would
> work, but I don't think that's it at all. He sticks to something simple,
and
> that's important - there are many mathematical systems that we wouldn't
> dream of using for databases, so there have to be some meta-criteria for
> selecting them. Topology? Statistics? While applicable to systems of
> systems, I think they're out of line for business apps.

You might be surprised if you start investigating the relationship between General Topology and Relational Model :-)

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Received on Wed May 12 2004 - 17:06:51 CEST

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