Re: Trying to define Surrogates
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Thu, 17 Aug 2006 16:40:48 GMT
Message-ID: <k_0Fg.50711$pu3.588455_at_ursa-nb00s0.nbnet.nb.ca>
>
> I think this is a fairly specific case where the natural key isn't
> easily manipulated, but it's a bit of a hack, and a fairly specific
> case. I think the more common use of a surrogate key is where no
> natural key exists - to separate cans of Campbell's chicken noodle
> soup, you need to give them an artificial label. This label sometimes
> makes it into the real world as well.
>
> In the case of fingerprints (a domain about which I'm speculating), I
> suspect that as implied by CSI there are specific points and tangents
> on the print that, collectively, act as a hash function to some numeric
> value. That value is derived entirely from the digital scan, and can be
> the key. The case of two fingerprints hashing to the same key would be
> a problem, of course - but probably no more than that of SSNs.
>
> Either way, the key would be not an identifier for the print, but
> derived directly from the print domain. That's different than a
> surrogate key as normally defined.
Date: Thu, 17 Aug 2006 16:40:48 GMT
Message-ID: <k_0Fg.50711$pu3.588455_at_ursa-nb00s0.nbnet.nb.ca>
erk wrote:
> JOG wrote:
>
>>My name is an identifier for me. >>My fingerprint is an identifier for me. >> >>Say we don't have the ability to digitise the photos we have of >>fingerprints. Then we produce: >> >>532673294 is a identifier for my fingerprint, which is a identifier for >>me. >> >>The 2nd level of indirection in the last line indicates use of a >>representative for an attribute that existed naturally before the >>design of the database. It is not that it is just wasn't 'familiar', it >>didn't exist at all - we have made the domain up specifically to >>facilitate the information modelling process. We have not just modelled >>the propositions we have added to them. >> >>That for me is the distinction made when I see the word surrogate in >>context of databases.
>
> I think this is a fairly specific case where the natural key isn't
> easily manipulated, but it's a bit of a hack, and a fairly specific
> case. I think the more common use of a surrogate key is where no
> natural key exists - to separate cans of Campbell's chicken noodle
> soup, you need to give them an artificial label. This label sometimes
> makes it into the real world as well.
>
> In the case of fingerprints (a domain about which I'm speculating), I
> suspect that as implied by CSI there are specific points and tangents
> on the print that, collectively, act as a hash function to some numeric
> value. That value is derived entirely from the digital scan, and can be
> the key. The case of two fingerprints hashing to the same key would be
> a problem, of course - but probably no more than that of SSNs.
>
> Either way, the key would be not an identifier for the print, but
> derived directly from the print domain. That's different than a
> surrogate key as normally defined.
It would, in fact, qualify as an 'intelligent key' with all the term implies. Received on Thu Aug 17 2006 - 18:40:48 CEST