Re: One-To-One Relationships

On Dec 2, 4:36 am, 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?
>
> -- Jan Hidders

Here in this tread it is about E/R and RM as well as relationship among them and I also used terms "entity" and "attribute". Many books about DB theory also describe connection between E/R and RM, so your question is absurd. I posted this in wish to explain to you some basic things through the example. I mean some basic things which nature you don't understand.

Vladimir Odrljin Received on Sun Dec 02 2007 - 18:53:43 CET