Re: One-To-One Relationships

On 2 dec, 19:40, Cimode <cim..._at_hotmail.com> wrote:
> On 2 déc, 16:11, Jan Hidders <hidd..._at_gmail.com> wrote:
>
> > 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.
>
> I am not assuming anything.

Good. Then the answer to your question is simple. If the entity doesn't have a name already in the UoD then it is better to not have a name to identify it in your model.

• Jan Hidders