Re: Normalizing the ER model

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