Re: the two questions

From: vldm10 <vldm10_at_yahoo.com>
Date: Fri, 23 Nov 2007 21:38:07 -0800 (PST)
Message-ID: <94522966-96c1-47e7-9f8b-96da1840ef31_at_b15g2000hsa.googlegroups.com>


On Nov 23, 10:36 pm, JOG <j..._at_cs.nott.ac.uk> wrote:
> On Nov 24, 12:38 am, vldm10 <vld..._at_yahoo.com> wrote:
>
> > Not long time ago on this NG there were few posts which involved an
> > entity with 200+ attributes.
> > Let all these attributes satisfy the following two conditions:
> > 1) All these attributes are mutually independent
>
> Then there are no functional dependencies so the entity can only be
> identified by the collection of all its attributes - and hence you'd
> end up with an equivalent superkey. If any of those attributes
> "change" it would also therefore be a different entity altogether.

It should be at least 400 attributes by my calculation. Are you familiar with "Temporal DB" theory?

>
> > 2) Every attribute of an entity can change its value - like in
> > "Temporal DB"
>
> Nope, not gonna squeeze that one past. If they are all unstable, well
> then, you are saying there is not a single attribute that is
> consistent over the entity's lifetime? In that case how could you
> ever identify it in the real world following change? Perhaps hire
> someone to follow it down the street continually pointing at it?
> Y'know, Its strange we don't get more of that in daily life, given the
> popularity of OID's in IT... oh well, I guess we're stuck with the old
> fashioned method of identifying things by looking at them.
>
>
>
> > Now I have two questions:
>
> > 1) How many attributes has a key of the corresponding relation?
> > 2) How many attributes has a key of m-n relationship between the two
> > mentioned entities?
>
> A binary relationship, without use of a surrogate, would obviously
> require twice the number of attributes that made up the aforementioned
> superkey.

This is m-n relationship and the key can have more attributes then you wrote.

>
> Hmmm, why do I get the feeling you're about to try and sell me
> something? ;)

This is about compex DB and some interesting cases about them. I beleive they will be actual in near future, people start to ask about it.

Vl. Odrljin

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> > Vladimir Odrljin- Hide quoted text -
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> - Show quoted text -
Received on Sat Nov 24 2007 - 06:38:07 CET

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