Re: A real world example

"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." 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.

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.

> Jim.
>
Received on Wed Aug 16 2006 - 20:19:35 CEST