Re: Entity vs. Table

Ben and Alan,

"Alan" <alan_at_erols.com> wrote in message news:2j5mp4Ft3gu0U1_at_uni-berlin.de...
>
> "ben brugman" <ben_at_niethier.nl> wrote in message

> > The fysical implementation, normaly does have
> > indexes, errorchecking bits and is often implemented
> > on a Raid. Therefore the implementation contains
> > redundancy. The fysical implementation therefore
> > is not 3NF, although it often is an implementation
> > of a logical model which should be 3NF.
> >
> > (By the way, indexes (which can be rebuild) are
> > definitely redundant information).
> >
> > ben
>
> I've been nice up till now, but I'm sorry- you clearly do not know what
you
> are talking about. 3NF has nothing to do with RAID, error checking bits,
or
> anything else that is not data. Indexes are not redundant information.
They
> are references. Indexes are analagous to looking in the index of a book.
You
> look there to get a specific place to look in the book. If indexes were
> redundant, they would serve no purpose. Indexes are part of the physical
> implelmetation, and have zero to do with the logical model, which is where
> you establish 3NF.

I honestly think the above disagreement between the two of you is caused by language confusion rather than substantive difference. In particular, I think that the word "redundancy" means different things to the two of you.

I think I understand what Ben is saying about redundancy and indexes, error checking and RAID. I think he means, roughly, that an index can be derived from the corresponding table, the error checking bits can be derived from the corresponding block, and the RAID set can be derived from one of the copies of it.

Both of you are saying that a system that contains indexes, error checking, or RAID does not necessarily violate 3NF, because 3NF pertains to the tables themsleves, and not to the support structure.

I think both of you know what you are talking about, but you aren't understanding the other one.

Or am I wrong? Received on Mon Jun 14 2004 - 15:47:25 CEST