Re: Normalization by Composing, not just Decomposing

"Jan Hidders" <jan.hidders_at_REMOVETHIS.pandora.be> wrote in message news:eAidc.64823$6j6.4312167_at_phobos.telenet-ops.be...
> Dawn M. Wolthuis wrote:
> >
> > If I am understanding correctly, the process of normalization for any
set of
> > data attributes is a process of decomposing from one large set to
several
> > smaller ones. That makes sense when starting from scratch.
> >
> > But tests for determining whether data is normalized also seem to focus
on
> > whether it has been fragmented sufficiently and do not take into account
> > whether the data has been TOO fragmented.
>
> Of course they take that into account! Except for the obvious
> requirement to be information preserving, you might have a requirement
> to be dependency preserving. Even beyond that the theory doesn't tell
> you when you should and should not split. It only tells you in what
> stage you are, what the potential problems in that stage are and how you
> might get rid of them. Whether you want to accept these potential
> problems is up to you as a database designer. But without a thorough
> understanding of normalization theory you cannot make a well-founded
> decision about this.
>
> By the way, if you think normalization for the 1NF relational model is
> tricky,

not sure I said that

> then I seriously doubt you will master the art for the NFNF
> relational model. Never mind a semistructured datamodel like XML or the
> Pick data model where things get much much more complicated.

Do you HAVE a description of any type of normalization or other data modeling theories related to PICK? I sortof think I'm at least in the 3.5 (tennis 5 point scale) camp on PICK data modeling & design and am working to take what I KNOW somewhere in the depths of my brain and formalize it so that it doesn't appear to relational theorists as beeing so loosely-goosey.

If someone has already done that -- PLEASE POINT ME TO IT! I know Dick Pick & Don Nelson did not do that, nor did some of the heavy-weights like Henry Eggers (who sortof gave me the blessing to go for it last year while sitting in a little cafe by the Pacific ocean with Jonathan Sisk, a fine PICK author and historian).

> > In other words, there ought to be some "rules" that govern when we ought
not
> > split out data attributes, in general, as well as when we should
decompose
> > them.
>
> That's what the rules already "do" now. If you want to be in 3NF / BCNF
> / PJNF / DKNF or whatever, and you can join two tables without breaking
> the NF requirements, then there is nothing in normalization theory that
> tells you to keep them separate.

But there is nothing that tells you to put them back together, right? You can obey all the rules of normalization and have a set of N resulting relations when someone else also has a normalized set of the same attributes but with N-500 relations, right? Again, I might very well be wrong on this point -- I want to know if I am. Thanks. --dawn

> In that respect they are much like
> physical laws: they don't tell you what to do, just what the
> consequences of your choices will be.
>
> -- Jan Hidders
Received on Thu Apr 08 2004 - 22:46:58 CEST