Re: One-To-One Relationships

On 5 dec, 15:45, vldm10 <vld..._at_yahoo.com> wrote:
> On Dec 4, 5:20 pm, Jan Hidders <hidd..._at_gmail.com> wrote:
>
>
>
> > On 4 dec, 21:55, vldm10 <vld..._at_yahoo.com> wrote:
>
> > > On Dec 3, 6:01 am, Jan Hidders <hidd..._at_gmail.com> wrote:
>
> > > > On 2 dec, 18:53, vldm10 <vld..._at_yahoo.com> wrote:
>
> > > > > 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?
>
> > > > > 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".
>
> > > > My remark that you responded to was only about ER modelling.
>
> > > I tried to explain my answer through an example.
>
> > You formulated the explanation of your answer to an issue in ER
> > modeling in RM terminology. If you would have formulated it in ER
> > terminology that might have helped you considerably to make your
> > point. RIght now I still don't have a clue what you are trying to tell
> > me or even whether it is actually relevant for the question at hand.
>
> > -- Jan Hidders- Hide quoted text -
>
> > - Show quoted text -
>
> Jim wrote "...... and identify them (entities) by one attribute..." and
> you asked "why by only one attribute? Why not by a set of
> attributes?"
> My objection here is related to misunderstanding what is identifying?
> What is construction to make entities to be distinct? What we use for
> identifying? What is difference between "distinguishing" and
> identifying? etc
> On your question "Why not by a set of attributes?" we not identify an
> entity I gave the answer: "This is OK, but my advice to you - don't
> use it often."
> To get clue I will gave you one example:
>
> During a phone call, we would never say the following: "May I speak
> with the 5 foot tall and has blue eyes and has brown hair and ..."
> Rather, we will say: "May I speak with John?"
>
> I wrote small theory about identifying and above example is from
> there. I already recommended you to read it (if you are interested?)
> You can find it on my website: www.dbdesign10.com
> look under the following: "7.1 Identifying the Plurality"
> I am not interested in further discussion about this.

*shrug* Suit yourself.

• Jan Hidders