Hi!
Thanks Kai for correction but some points:
When designing a n:m-relation this approach doesn't work. You need
a third table between the two that have been modelled.
Yes, i know it, but it is just a problem of realization. For example, for
this case after defining
Many-to-many relation, the user can define in properties a table, which can
be a "third table", or leave the
name which will be suggest by the application.
And one more time about ERD. I see it like a graphical representation of a
data model of an application. Having the possibility
of creating ERD, the user can see the db structure of the application. And
having special stereotype in a class diagram, the user can
see what classes are entities.
Having only special stereotype in a class diagram can make many problems and
can be not very flexible to use because imagine you
have an entity which has fields, that are not storing in the db, so you need
to have an ability to define columns, and you will do it in a Class diagram.
I think it is a wrong way.
By having ERD you just connect classes in Class Diagram to Entities in ERD,
and in ERD you define everything you need for db.
IMHO it is more flexible and appear to be a better solution.
What do you think about it?
On 3/27/07, Kai Drahmann <[EMAIL PROTECTED]> wrote:
Hi,
I'm currently working on argouml-sql. Since I had the same ideas (and
made some mistakes) when beginning I think I need to correct some
points: (see below)
Am 25.03.2007, 14:10 Uhr, schrieb nett .by <[EMAIL PROTECTED]>:
> Hi Linus!
>
> I will try to describe my idea with more particular:
>
> Entity Relationship Diagram (ERD) is a type of diagram, where you
> describe
> the db structure:
> -Every entity in this diagram is a separate table in db
When designing a n:m-relation this approach doesn't work. You need
a third table between the two that have been modelled.
> -In every entity you can specify columns and types of columns
> -You can define primary keys and foreign keys
Foreign keys are not part of an entity relationship diagram. They
occur in relational models.
> -You also can specify One-to-One, One-to-Many or Many-to-Many
> Relationships between entities
When modelling an ERD you can do it. When modelling a relational
model n:m-relations simply don't exist.
There are three types of data models:
1. Conceptual model - entity relationship diagram for example
2. Logical model - relational model or network model for example
3. Physical model - model used by DBMS for data storage - contains
indices for example
As Tom Morris stated in another post an UML class diagramm corresponds
to an entity relationship diagram - the only difference is that another
notation is used.
Kai
> -etc.
>
> After creating Entity Relationship Diagram you can generate db by
> choosing
> db type (additionally indicate or load driver for this db).
> You also can reverse existing db into ERD by connecting to db, choosing
> db
> tables and represent them in ERD.
>
> One more very good feature, i think, will be the generation of class
> diagram
> from ERD, or generating ERD from class diagram.
> This will help to accelerate the application development which use data
> bases.
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