Re: Normalizing the ER model
From: Finarfin <finarfin_at_sympatico.ca>
Date: Fri, 22 Nov 2002 00:40:10 -0500
Message-ID: <wsjD9.10078$7X4.1229953_at_news20.bellglobal.com>
>
> 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
Date: Fri, 22 Nov 2002 00:40:10 -0500
Message-ID: <wsjD9.10078$7X4.1229953_at_news20.bellglobal.com>
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. >> >> -- 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
An excellent discussion of the E/R model is given in C.J. Date's An Introduction to Database Systems, chapter 13. This book addresses clearly each of your questions. Of particular note is this item from the chapter summary:
- Use the E/R approach to generate "large" relvars representing regular entities, weak entities, etc., and then
- Use the ideas of further normalization to break those "large" relvars down into "small" ones.
JE Received on Fri Nov 22 2002 - 06:40:10 CET