Re: Pizza Example
Date: Sat, 24 Apr 2004 14:23:49 GMT
On Sat, 24 Apr 2004 09:45:20 -0400, "Laconic2" <laconic2_at_comcast.net> wrote:
>> But if you have an ER model you don't have a database design.
>That's the whole point. The ER model is useful for what it doesn't say, as
>much as for what it does say.
IMO it is unuseful and harmful because it can not say many things.
> It does establish the connection between the
>data, expressed in values and domains, and the subject matter, expressed
>in entities, relationships, and attributes.
It forces us to distinguish between entities and relationships without any sound criteria.
>It requires a little work to turn this into either a relational model or a
>CODASYL model, but you haven't hidden the design decisions in the ER model,
>where they are hard to see.
But the result is poor in most cases.
If you start directly designing a relational database, it is a lot easier to get a good design.
>>You can not turn a relational database design in a ER model in almost all
>I didn't get this point. What are you saying?
That you can not represent most busines rules with an ER model. If you try to turn a relational database design into an ER model you will lose a lot of information.
Alfredo Received on Sat Apr 24 2004 - 16:23:49 CEST