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Re: Database design, Keys and some other things

From: mAsterdam <mAsterdam_at_vrijdag.org>
Date: Fri, 30 Sep 2005 10:06:02 +0200
Message-ID: <433cf1d0$0$11072$e4fe514c@news.xs4all.nl>


Marshall Spight wrote:
> JOG wrote:

[snip]

>>A VIN exists in the real world, and as such is part of the proposition
>>we are encoding. A surrogate key is an artifice of the database, does
>>not exist in the world you are modelling, and is implemented to get
>>your system working. This seems a very clear distinction to me.

>
>
> Perhaps we have different definitions of surrogate keys. The VIN
> may be something that's not a surrogate key in database A, but
> it's certainly a surrogate key in *some* database, and hence I
> don't see any particular difference between it and any other
> made-up identifiers. SOMEone, some database, made up the VIN
> out of thin air; we could well say they "implemented [it] to get
> [their] system working." So I still don't see the distinction
> you're drawing here.

There is an important difference. Unless we are talking about that specific "*some*" database, the VIN is /not/ a surrogate key in the database at hand.
A while ago we had some discussion as to wether an url is a key or not. My stance on that was: only if the content is in our database the url may be a key, so - in general: an url is not a key. There is a similar distinction to be made here. In general, a VIN is not a surrogate key (though it is in the "*some*" database - only there).

>

>>I disagree
>>wholeheartedly with you that the philosophy of what information
>>actually is, and the consequences that may have for encoding and
>>manipulation of it, is irrelevant to database theories.

>
>
> I don't believe I ever took that position.
>
> However, there is a definite trap in this general area, which
> is the trap of thinking that there is anything profound to
> be said about the relationship between the internal and the
> external predicate. That relationship, between the database
> and the world it models, exists only in the minds of the users
> of the system, and it is wholly an illusion, if you will.
> This is an important point, and it is also a philosophical one.
Received on Fri Sep 30 2005 - 03:06:02 CDT

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