Re: One-To-One Relationships
Date: Sun, 2 Dec 2007 11:28:51 -0800 (PST)
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..._at_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
> > > > > 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.
> > 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.
Algebra did not exist at the time of Aristotle...If I were too give *any* credit to entities it would certainly not be in a metaphysical sense but as a possible synonym for mathematic *unkown values* that ought to be caracterized though some kind of structuring or refining to be determined. That is at least how they were refered to by the inventors of algebra... Received on Sun Dec 02 2007 - 20:28:51 CET