Re: the two questions
Date: Mon, 26 Nov 2007 14:47:36 GMT
"Brian Selzer" <brian_at_selzer-software.com> wrote in message
> "David Cressey" <cressey73_at_verizon.net> wrote in message
> > "Brian Selzer" <brian_at_selzer-software.com> wrote in message
> > news:Dj92j.77429$Um6.17027_at_newssvr12.news.prodigy.net...
> >> "JOG" <jog_at_cs.nott.ac.uk> wrote in message
> >> > 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
> >> are identical--unless, of course, one of the attributes is a surrogate;
> > Do you mean "surrogate" or "synthetic" ?
> I don't know what you mean by "synthetic." What I mean by a surrogate is
> value that always refers to a particular individual and can never refer to
> any other individual. How it comes into being is irrelevant.
The term "surrogate", as I have seen it used has the features you state. But a "surrogate key" also has two other features that you may or may not intend in this discussion. First, it is (or should be) never exposed to the users. Second, it is a substitute for some "real key" that is not used bacause the data source has incomplete knowledge concerning the real key, and this incomplete knowledge would cause a failure of identification in some situations.
The term "synthetic key" is one I have only seen in this newsgroup. what it means, AFAIK, is a key that is just as visible as a natural key, but assigned to a particular individual, rather than being a natural attribute of that individual. So a person's fingerprints might be a natural key (provided it works as a key), but a person's "personal ID number" would be a "synthetic key".
I've also seen the term "artificial key" used in the same sense as
Anyway, the distinction I'm asking you to make is this: do the users use
the value to refer to a particular individual, or does the system use it in
this manner, under the covers? This distinction is meaningful, I believe.
Anyway, the distinction I'm asking you to make is this: do the users use the value to refer to a particular individual, or does the system use it in this manner, under the covers? This distinction is meaningful, I believe.
Received on Mon Nov 26 2007 - 15:47:36 CET