Re: One-To-One Relationships

From: David Cressey <>
Date: Fri, 30 Nov 2007 18:45:06 GMT
Message-ID: <SSY3j.13$xB.5_at_trndny06>

"JOG" <> wrote in message
> On Nov 30, 6:03 pm, Tegiri Nenashi <> wrote:
> > On Nov 30, 8:19 am, Jan Hidders <> wrote:
> > The distinction between entities /
> >
> > > relationships, domain objects / predicates is pretty well-established
> > > in linguistics, philosophy and logic.
> >
> > That certainly means you can define them formally in database terms,
> > right?
> > Here is one such
> > It defines an entity as a relation (aka table:-) with a single
> > noncomposite key, and relationship as a table with composite key. Does
> > this definition pretty much exhausts the entity-relationship theory?
> I like the insight that both 'entities' and 'relationships' are
> subtypes of a parent concept, that is simply a set of attributes and
> values. I'd like to see a formalization of that which doesn't rely on
> relational theory and the concept of keys however, even though I
> imagine there would be a direct correspondence.

Here's the way I would try to unify the two concepts. Relationships can be binary, ternary, and so on, depending on the number of entities involved in a single instance of the relationship. How about considering an entity a "unary relationship"?

I would disagree with "set of attributes and values". I think that "attributes, values, and domains" are where one begins to stop talking about the "real world" as such, and begin to talk about the data that is claimed to describe the real world.

Note that "attributes, values, and domains" are common elements to the ER model and to the relational model. They provide a brdige from one kind of modeling to the other. Received on Fri Nov 30 2007 - 19:45:06 CET

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