Re: Normalizing the ER model

"Jan Hidders" <hidders_at_REMOVE.THIS.uia.ua.ac.be> wrote in message news:3dde69b0$1_at_news.uia.ac.be...
> K.Y. Fung wrote:
> >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.
> >
> >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.
>
> Most ER models allow yout to specify keys and it is good practice to do
so.
> They are part of the constraints you should specify.
>
> >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?
>
> Take a look at ORM where you can even have key constraints over
> relationships. If you can have those you can also have dependencies inside
> relationship and therefore it can be interesting to check if some
> normalization needs to be done there.
>
> -- Jan Hidders

Hi Jan,

I like ORM because of the contraints one can apply to relationships. But in my experience, these constraints are usually implemented by stored procedures or some other procedural logic. So what does normalization have to do with it?

 Best Regards,
Greg Received on Fri Dec 06 2002 - 23:54:12 CET