Re: Importance of the normal forms

> What people *should* do is check if they can proceed
> to BCNF and 4NF and still remain
> dependency preserving.

Hi, sorry to jump in, but I'm struggling with all this 3nf/BCNF stuff. When you say "proceed" to BCNF, I was under the impression the BCNF was "less" normal than 3nf. That is, the FDs and CKs replace the need for some table splitting. When you go from 3nf to BCNF are you typically creating more tables or fewer? BTW, If I'm sounding really stupid, it's because for the most part I am.

Thanks,
Seth

"Jan Hidders" <hidders_at_REMOVE.THIS.uia.ua.ac.be> wrote in message news:3dd4370e$1_at_news.uia.ac.be...
> Juan Pardillos wrote:
> >
> >I'd like to know which formal forms are the most important, both from
> >a theoric point of view and from a practical point of view. I mean, is
> >enough with considering BCNF or we should go on, if possible to get
> >4FN or more?.
> >
> >Which is the usual way of proceeding?.
>
> The usual way is that many people stop at 3NF because they were taught
that
> this the most practical NF and if you go any further things get too
> difficult, or too inefficient, or "overnormalized" or whatever. What
people
> *should* do is check if they can proceed to BCNF and 4NF and still remain
> dependency preserving. Sometimes this will make certain queries harder to
> compute, especially those that have to join again the tables that were
split
> in the normalization process, but whether this is significat may depend on
a
> lot of details and on the other hand not normalizing can maked queries
> harder if they do not need the join. Moreover, not being in 4NF can
> cause lots of redundancy and make your tables much bigger then necessary.
>
> >As an student, I've been only taught until 4FN, but I think there are
> >some more. I'd like to know if they are really important and/or easy
> >to understand. Any link is greatly appreciated.
>
> There's only one more, 5NF (also called PJ/NF or PJNF or the project-join
> normal form), and it has in fact been proven that this is the
> highest normal form that can be reached by splitting relations by
> decomposing them into projections. For a small example see:
>
> http://www.gslis.utexas.edu/~l384k11w/normover.html
>
> It's one of the hardest normal forms to understand and in practice it is
not
> easy to spot the special type of dependencies, i.e., the join
dependencies,
> that are used to check if you are in 5NF. In fact, it is a public secret
> that there are a few text books out there, some of them by well-known
> authors, that don't define it correctly.
>
> -- Jan Hidders
>
>
Received on Mon Nov 18 2002 - 23:33:21 CET