Re: domain questionnaire

JRStern wrote:
> On Fri, 23 Feb 2001 23:22:26 GMT, "Scot A. Becker"
> <scotb_at_inconcept.com> wrote:
> >Ummmm... A few points from an admitted ORM bigot....
 

> >1) I would hesitate to call ORM "a dialect of entity-relationship models".
> >ER modeling models entities, attributes, and relationships between entities.
> >ORM models obects and the roles they play with other objects.
>
> Role == Relationship?

In ORM they call a relationship a 'fact type' and entities are called 'object types'. The 'role' is the role that an object plays in a fact type. For instance, if you have a 'parent-of' fact type then you will have the roles 'parent' and 'child'.

> >There are no
> >attributes, and the elementary fact concepts ensure normalization.
>
> Heh-heh. Good trick, without attributes. Or even with them. We all
> know normalization is trivial, right?

Well, the explicit search for atomic/elementary fact types is a very good method to get as normalized as possible in a very intuitive way. I think it is one of the best ways to explain intuitively what is going on when you are normalizing.

As far as the absence of attributes is concened, I am still not very sure whether that is really true. In some sense ORM does have attributes but they call them fact types between lexical and non-lecial object types, but these are drawn in the same way as other fact types. So in that sense you only have relationships/fact types and no attributes.

-- 
  Jan Hidders