Re: One-To-One Relationships

On 2 dec, 14:16, Cimode <cim..._at_hotmail.com> wrote:
> On 2 déc, 10:36, Jan Hidders <hidd..._at_gmail.com> wrote:
>
> > On 1 dec, 06:26, vldm10 <vld..._at_yahoo.com> wrote:
>
> > > On Nov 30, 9:34 am, Jan Hidders <hidd..._at_gmail.com> wrote:
>
> > > > Why by only one attribute? Why not by a set of attributes? Or a
> > > > combination of attributes and relationships (as is the case for weak
> > > > entities)?
>
> > > This is OK, but my advice to you -don't use it often.
> > > I will give you one example:
> > > The relation has A1, A2, A3, A4 "attributes" and they are mutually
> > > independent (i.e. they are in BCNF)
> > > The "attributes" can change their values for "entity" like in
> > > "temporal DB". User needs on line all information for any "entity" in
> > > any moment.
> > > Can you please write the key for this relation so that we can discuss
> > > it.
>
> > You do realize we were talking about ER modeling, not RM modeling,
> > don't you?
>
> I am talking about neither of the two. If you ask me, I place terms
> like *entity* on the same level than terms like *object*: too
> subjective to be reliable to build logical reasonning onto.

Any data model is to some extent subjective since it represents the universe of discourse of a certain group of people. Of course the representation of that data models should be exactly defined, but that doesn't require that the notion of entity is more defined than it is now.

> But I should phrased my question otherwise: what's more elementary/
> best than a name to identify an entity, any entity ?

Your question seems to assume that all things that we can speak about always have a unique name. For a particular universe of discourse that may or may not be the case.

• Jan Hidderes