Re: Normalizing the ER model

"K.Y. Fung" <kyfung_at_hotmail.com> wrote in message news:c22bb40d.0211211822.2bb16043_at_posting.google.com...
> hidders_at_hcoss.uia.ac.be (Jan Hidders) wrote in message
news:<3dda1122$1_at_news.uia.ac.be>...
> > In article <6278687.0211181428.75890385_at_posting.google.com>,
> > Juan Pardillos <sicotom_at_eresmas.com> wrote:
> > >
> > >is it possible to apply the normalization process directly to the ER
> > >model instead of apply it to the relational model?
> >
> > Yes, you can interpret a relationship as a relation and then apply the
usual
> > normalization rules. The same holds for the entity types but you have to
> > take care of where the connections with the relationships go if you
split
> > then entity.
> >
> > -- Jan Hidders
>
> I am just a beginner studying the process of normalization in OU Hong
> Kong. I don't understand how normalization can apply to ER model.
>
> Correct me if I were wrong. ER model consists of Entity diagram,
> Entity type and its headings, Constraints and Assumptions. But Entity
> type only have an identifier without any keys. Entity type only shows
> there is a need to record information, and we draw a relation between
> entities base on the requirement we gather from user. But neither the
> entity heading nor the relation tell us how information in one entity
> is related with information in another entity. We can only infer it in
> the relational model when primary key / foreign key mechanism comes
> in. So how can normalization apply to ER model?
>
> Regards,
> King Yin Fung
>

King Yin Fung has it right. . Normalization is applied to attributes, not entities. Much of what falls out of normalization are new entities. As a matter of fact IDEF requires only identifiers for a "complete model" at the conceptual level. Normalization, IMHO, removes update anomalies. I usually only go to 3rd normal form. What ER modeling provides for me is migration of key/foreign key from on entity to another. But then, still, you must go through a final normalization .

Regards,
Greg Received on Fri Dec 06 2002 - 23:41:13 CET