Re: One-To-One Relationships

From: vldm10 <vldm10_at_yahoo.com>
Date: Tue, 4 Dec 2007 12:55:30 -0800 (PST)
Message-ID: <78acb467-3d08-4530-afb5-f01cba4410b2_at_b40g2000prf.googlegroups.com>


On Dec 3, 6:01 am, Jan Hidders <hidd..._at_gmail.com> wrote:
> On 2 dec, 18:53, vldm10 <vld..._at_yahoo.com> wrote:
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> > On Dec 2, 4:36 am, Jan Hidders <hidd..._at_gmail.com> wrote:
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> > > On 1 dec, 06:26, vldm10 <vld..._at_yahoo.com> wrote:
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> > > > On Nov 30, 9:34 am, Jan Hidders <hidd..._at_gmail.com> wrote:
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> > > > > 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)?
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> > > > 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.
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> > > 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".
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> My remark that you responded to was only about ER modelling.
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> -- Jan Hidders- Hide quoted text -
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> - Show quoted text -

I tried to explain my answer through an example. But it is not so important. By the way, you can find the good answer on your question "Why by only one attribute? Why not by a set of attributes? " on my website www.dbdesign10.com look under the following: "7.1 Identifying the Plurality"

Vladimir Odrljin Received on Tue Dec 04 2007 - 21:55:30 CET

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