Re: Does Codd's view of a relational database differ from that ofDate&Darwin?[M.Gittens]

From: Jon Heggland <heggland_at_idi.ntnu.no>
Date: Tue, 5 Jul 2005 12:41:16 +0200
Message-ID: <MPG.1d346f50e54759779896dd_at_news.ntnu.no>


In article <7_gye.137288$UA5.7335985_at_phobos.telenet-ops.be>, jan.hidders_at_REMOVETHIS.pandora.be says...
> > 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?

Everything you can do with an OID / opaque key, you can do with a (surrogate) key.

> >>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.

Sure. In that case, I would choose something else to identify myself by. That is neither here nor there. I don't use the same database for all applications.

> > 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.

If you say so... but are you saying the string "Jon Heggland" can't represent me?

-- 
Jon
Received on Tue Jul 05 2005 - 12:41:16 CEST

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