Re: One-To-One Relationships

On 2 déc, 16:03, "David Cressey" <cresse..._at_verizon.net> wrote:
> "Cimode" <cim..._at_hotmail.com> wrote in message
>
> news:36f20483-5085-4d52-b33d-1ddd85bd6735_at_w56g2000hsf.googlegroups.com...> On 30 nov, 19:33, JOG <j...@cs.nott.ac.uk> wrote:
> > > On Nov 30, 6:03 pm, Tegiri Nenashi <TegiriNena..._at_gmail.com> wrote:
>
> > > > On Nov 30, 8:19 am, Jan Hidders <hidd..._at_gmail.com> 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
>
> attempt:http://arxiv.org/PS_cache/arxiv/pdf/0710/0710.2083v1.pdf
>
>
>
> > > > 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.
> > OK I will play devil's advocate and try to believe that entities could
> > be an alternative expression of entities...
>
> > Quite frankly, I understand the intent but not the need to
> > differentiate relations and entities...
>
> > I believe somehow that because Relations rely on set theory and
> > relational algebra, it simply has a longer mathematical history and de
> > facto more abstract tools concepts to work with than Entities that
> > seem recent. I do believe that the keys was simply Codd's way to
> > express *identifiablity* in a way that his IBM audience could be
> > receptive to the rest of the model...I do not perceive keys as a
> > sufficient reason to require differentiation between the two models...
>
> Entities are not recent. Entities are as old as Aristotle. Aristotle was
> not attempting to design databases. Codd was not attempting to reformulate
> the metaphysics of how we understand reality.
Codd was doing math not Aristotle...;)

> Chen's contribution was to provide a model in which the information
> requirements can be stated without presupposing a design that is going to
> meet those requirments.
So ? Received on Sun Dec 02 2007 - 20:13:12 CET