Re: the two questions

On Nov 25, 6:29 pm, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
> David Cressey wrote:
> > "Brian Selzer" <br..._at_selzer-software.com> wrote in message
> >news:Dj92j.77429$Um6.17027_at_newssvr12.news.prodigy.net...
>
> >>"JOG" <j..._at_cs.nott.ac.uk> wrote in message
> >>news:8505d954-cdc3-4bf8-9107-b307563be0e8_at_r60g2000hsc.googlegroups.com...
>
> >>>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 cannot be determined whether two representations from two distinct
>
> > points
>
> >>in time refer to the same individual--even if all of the attribute values
> >>are identical--unless, of course, one of the attributes is a surrogate;
>
> > Do you mean "surrogate" or "synthetic" ?
>
> Actually, what he is saying is at least one attribute must remain the
> same. Whether that attribute is a surrogate is a red herring.

Spot on.

>
> Suppose two tuples differ completely except for one attribute you know
> was assigned arbitrarily. How do you know they are really the same
> thing? After all, all observable properties have changed. The fact that
> an arbitrary number is the same doesn't really tell us much.

Unless someone tattooed it to their posterior of course. Mine's certainly not observable. Received on Mon Nov 26 2007 - 01:05:03 CET