Re: Does Codd's view of a relational database differ from that ofDate&Darwin?[M.Gittens]
From: Jan Hidders <jan.hidders_at_REMOVETHIS.pandora.be>
Date: Mon, 04 Jul 2005 20:28:51 GMT
Message-ID: <7_gye.137288$UA5.7335985_at_phobos.telenet-ops.be>
>
> A surrogate key means what the database designer states that it means,
> just like any other element of the model. It is not logically different
> from an OID or an "opaque key", except that it is handled without
> introducing special operators and restrictions.
>
> No, but for the purpose of a particular database, I might very well be.
Date: Mon, 04 Jul 2005 20:28:51 GMT
Message-ID: <7_gye.137288$UA5.7335985_at_phobos.telenet-ops.be>
Jon Heggland wrote:
> In article <BUAxe.135753$ms1.7223342_at_phobos.telenet-ops.be>,
> jan.hidders_at_REMOVETHIS.pandora.be says...
>
>>> >>>I don't see where hand-waving and informality enters into it. >> >>In the part where you forget to explain what "surrogate" exactly means.
>
> A surrogate key means what the database designer states that it means,
> just like any other element of the model. It is not logically different
> from an OID or an "opaque key", except that it is handled without
> introducing special operators and restrictions.
If it has different operators and different restrictions associated with it, how can it then be logically the same?
>>Yes, they can, but that is neither here nor there. Lexical objects are >>identical to their representation, non-lexical objects are not equal the >>combination of lexical objects they are identified by. If you are >>identified by the string "Jon Heggland" then that is not the same as >>saying that you are identical to that string.
>
> No, but for the purpose of a particular database, I might very well be.
Sure. But for the purpose of another database you might very well not be.
> And anyway, if I am identified by an OID or opaque key, then that is not
> the same as saying that I am identical to that OID or opaque key. What
> is the difference?
An OID doesn't identify you, it represents you. That's a different kind of relationship.
- Jan Hidders