Re: Normalisation
Date: Sat, 9 Jul 2005 14:04:03 +0200
Message-ID: <MPG.1d39db91cfb57ad59896f2_at_news.ntnu.no>
In article <xfCze.140548$uH4.7139418_at_phobos.telenet-ops.be>,
jan.hidders_at_REMOVETHIS.pandora.be says...
> >>>A set can be transformed into a unary relation with a simple operation.
> >>>A string can be transformed into a binary relation (integer and
> >>>character) with a simple operation.
> >>
> >>That requires logarithmic space, and not constant space as my
> >>transformation. So it is arguably more complex.
> >
> > Please elaborate. Assuming for the sake of the argument that you are
> > right, so what?
>
> It indicates that in one case there is a larger similarity than in the
> other because you meed more work to do the transformation. You're not
> asking me to explain the stated complexity classes of the operations,
> are you?
Well, yes, I actually am. Sorry if it is trivial, but I don't see the difference. Or the logarithm.
Anyway, that is an implementation matter. The transformation at the logical level is trivial.
> Usually it is relatively well-known which operations are possible in a
> DBMS and which aren't. That makes it in practice actually a quite stable
> notion even though it is a relative one.
> > It is also rather
> > complicated, imo, since you have to refer to operations over signatures
> > and proper classes as opposed to sets/domains.
>
> The definition does not refer to proper classes, and it is always a bit
> dangerous to call something complicated just because you had trouble
> understanding it. :-)
Complexity can be measured pretty objectively, no? :)
> As any good database researcher
How do you know I'm any good? :)
> you probably know
> and understand the notion of "genericity". Just as a test to see if you
> really understood it, can you tell me the relationship between this
> notion and the notion of 1NF I defined?
> I think the situation is a bit more complex than that. For me there are
> actually two logical levels: one at the conceptual level and one at the
> external level (as defined in the ANSI/SPARC model). For the external
> level I would agree that the form of the data model should be dictated
> by purely logical arguments. It should simply properly model how the
> users see their data. No more, no less.
>
> However, at the conceptual level the task of the model becomes more
> complex. Its job is to unify all the different models of the different
> user groups, but in a relatively implementation independent way. That
> means, for example, that if two groups want to nest the relations
> differently, then they probably should be modeled at this level by flat
> relations. It is for this level that I think 1NF is still useful.
Fair enough, I guess.
-- JonReceived on Sat Jul 09 2005 - 14:04:03 CEST