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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: Linkbases, Topic Maps, and RDF Knowledge Bases -- help me
On Tue, 10 Apr 2001, Uche Ogbuji wrote:
> > I think one common example of ternary relationship is the supplier kind
> of
> > relationship. It is something like (not very sure of the exact one)
> > m suppliers supply n products to p cities.
> >
> > I think the following is allowed in ODMG:
> >
> > class supply {
> > relationship Supplier supplier;
> > relationship Product product;
> > relationship City city;
> > }
>
> Either I'm missing something, or you're still mixing up N-ary
> relationships with binary relationships of greater than unit cardinality.
>
> Your ODMG example, for instance, is most certainly not an N-ary
> relationship. The relationship is from supply to suppiler, from supply to
> product and from supply to city. There is no relationship between, say
> city and product or vice versa.
>
> Once again, ODMG cannot express N-ary relationships.
Sorry for the delayed response. I was not very well over the last couple
of days. Also I think we can move it to one-on-one conversation regarding
this?
In the example, supply conceptually represents a relationship.
Yes, I think I see your point, you can say that a ternary relationship is
represented in ODMG as 3 binary relationships. There is no explicit
support for N-ary relationships in ODMG. Therefore ODMG cannot express
N-ary relationships. But this is the case because there is no difference
between the representation of a relationship and an entity -- it is the
same in relational model or ODMG model. But in ER, we have a difference in
representation - an entity is a rectangle, and a relationship is a
diamond.
Am I on the same track as you now?
Also one thing which I was wondering was do people use UML for data
modeling? I think ER is the tool, UML is just more like a programming
model.
regards - murali.
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