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?
Received on Sun Dec 02 2007 - 03:36:56 CST
