Re: A real world example

"Brian Selzer" <brian_at_selzer-software.com> wrote in message news:XkJEg.10231$o27.1677_at_newssvr21.news.prodigy.com...
>
> "JOG" <jog_at_cs.nott.ac.uk> wrote in message
> news:1155746467.961871.76490_at_b28g2000cwb.googlegroups.com...
>> Bob Badour wrote:
>>> [snip]
>>> By accepting his misuse of vocabulary, you encourage and legitimize the
>>> illegitimate while you interfere with communication and comprehension.
>>> Is it your goal to understand theory or to market the services of
>>> ignorants at the expense of their potential clients and other
>>> stakeholders?
>>
>> Of course not. All corrections are welcomed Bob.
>>
>>> [snip]
>>> I disagree that the concept of surrogate vs. natural is useful. A
>>> natural key is merely a familiar surrogate.
>>
>> By this I am unclear what a natural key is a surrogate for. If you
>> could spend some time expanding this definition, or referencing it, I'd
>> appreciate it.
>>
>>> The self-aggrandizing
>>> ignorant now has you redefining terms to make "surrogate" synonymous
>>> with "stable" and to make "natural" synonymous with "unstable".
>>
>> Piffle, bob. I have not adopted any of his terminology in my effort to
>> engage him, and you are misrepresenting my understanding of terms.
>>
>> I view a surrogate as a 'substitute' for an unrecordable distinguishing
>> attribute or set of attributes. This is the only logical definition
>> that I am currently happy with. It does not require stability by
>> definition, and I have only ever stated that stability is an attractive
>> quality and hence often appropriate to good design. That's my current
>> standpoint, and so that is what should or should not be criticized.
>>
>> Nevertheless I do not think you understood where Brian's mistakes stem
>> from, and that's what I have been looking for. It appears to be a
>> fundamental difference in what he views _identity_ to be. If the OP
>> does not maintain this basic concept of identity as we do (and as Codd
>> and Liebniz did) then there is little point in debating natural or
>> surrogate keys with him at all. The problem goes far deeper than that.
>>
>
> This thread started out because I objected to Bodour's statement, "natural
> keys are just familiar surrogates."

All you had to do to prove him wrong was to provide an example of a natural key that is not a familiar surrogate.

> That goes counter to the understanding
> I've held for years, that is supported by both Codd and Date. Codd used the
> term "permanent" to describe surrogates. Date implied permanence also by
> describing a surrogate's value as one that has never been used and will
> never be reused. Therefore, when I think of a surrogate key, I think in
> terms of permanence, not just stability.

Neither Codd nor Date suggested the "permanence" of surrogate values, but the permanence of the surrogate key.

>
> Do you agree that in one relation value a candidate key value can identify a
> tuple?
>
> Do you agree that a relation schema can have more than one candidate key?
>
> If only one candidate key value is different in successive relation values,
> can the others identify corresponding tuples in both relation values? I
> guess more importantly, do you think that the tuples correspond?
>
> If tuples can correspond in successive relation values that have multiple
> candidate keys where at least one remains constant, then why can't they
> correspond in successive relation values where none remain constant? What
> is being identified by corresponding tuples in successive relation values
> that have more than one candidate key where only one of the values have
> changed? The tuple? No, I don't think so. I think that it is the thing
> that the corresponding propositions are referring to.
> This is the source of the confusion. This is the impetus of my argument.
> If the thing that is indirectly identified by a candidate key can have its
> appearance altered without altering its identity (which must be possible if
> tuples that are different can correspond), then it is possible to have
> tuples in successive relation values that should correspond but don't. This
> is why I'm arguing for some mechanism to guarantee the ability to correlate
> tuples.

So you are arguing for tuple identifiers rather than a candidate key. Here is an old post that references the quote on the distinction: http://groups.google.com/group/comp.databases.theory/msg/bab7d889d157f137

>
>> Jim.
>>
>
>
Received on Wed Aug 16 2006 - 21:15:11 CEST