From: paul c <>
Date: Sun, 26 Sep 2010 23:11:45 GMT
Message-ID: <RqQno.1019$u9.505_at_edtnps82>

On 26/09/2010 2:16 AM, Erwin wrote:
> On 25 sep, 22:41, Brian<> wrote:
>> The employee named paul c fills the position named toilet scrubber.
>> Let's look at the information conveyed by this statement:
>> 1. there is an employee named 'paul c.'
>> 2. there is a position named 'toilet scrubber.'
>> 3. the named employee fills the named position.
>> Now, suppose that paul c's position changes from toilet scrubber to
>> floor sweeper.
>> Assuming that no other proposition references an employee named paul c
>> or a position named toilet scrubber, doesn't the denial of
>> (a) The employee named paul c fills the position named toilet
>> scrubber.
>> also deny that there is an employee named paul c and that there is a
>> position named toilet scrubber?
> Who again was it that should go back to school and take a course in
> logic ?
> EXISTS employee : employee(name) = 'paul c'&& employee(position) =
> 'toilet scrubber' does indeed imply EXISTS employee : employee(name)
> = 'paul c'&& EXISTS employee : employee(position) = 'toilet
> scrubber'. But note that the former and the latter are not
> equivalent, since the former conveys the extra information that the
> two properties apply to the very same person.
> NOT EXISTS employee : employee(name) = 'paul c'&& employee(position)
> = 'toilet scrubber' ===
> FORALL employee : NOT(employee(name) = 'paul c'&& employee(position)
> = 'toilet scrubber') ===
> FORALL employee : employee(name)<> 'paul c' OR employee(position)
> <> 'toilet scrubber')
> The denial of "(a) The employee named paul c fills the position named
> toilet scrubber." implies merely that if an employee is named paul c,
> then he is not a toilet scrubber, and also that if an employee is a
> toilet scrubber, then he is not named paul c.
> So the answer to your question "doesn't the denial of ... also
> imply ..." is, "No, doesn't.".

Also, the statement "there is a position named 'toilet scrubber'" (or suchlike but even if I remember it wrongly is reminiscent of how toilets relate to the current thread drift) is a tautology as far as the original db fragment is concerned, dressed up in invisible clothes, parading as an inference. It's no more pertinent, nor an inference, than "there is a number named 3". It's not necessary to conceive a relation in order to state it, a domain suffices. Actually the statement is about as useful to this db fragment as a domain of manures.

It makes me nostalgic for the irrelevant non-sequiturs, twists, turns and illogical trysts of the late Dawn W because hers had a screwball innocent charm that's missing here, oh well. (I don't mean this to be sarcastic, although I was tempted to go further when I first started typing!)

Meanwhile, one big obstacle from the original scenario, "a labour activity date must not change", remains unexplained and unjustified and mystical to me. Mystical because it's undersimplified, undersimplified because completely bald starting points can't be refined. We still don't know whether it is some misapprehension of trivial FD's, some new notion of constraint applied to transactions instead of relations or just bald nonsensical technocratic-sounding mumbo-jumbo, or something else (if there can possibly be anything else). I put this down to wanton, willful sloppy language use, even though there newsreaders that object to 'labour' but not to 'trival' might give some the illusion that what they wrote makes sense.

Still, this thread has had some value for me, reminding me of the only time I ever heard Codd speak and being puzzled why he seemed to be so obsessed about Christy Brinkley's telephone number. It took me some time to conclude that what he meant was that before all else, we must first agree on what we are talking about before we can start saying things (about it). Since then, keys have become a bigger and bigger obsession for me, very central for me now where db relations are concerned. At one time I couldn't reconcile them with the many mystics in this field who seem to conceive the propositions they come up with via some kind of physical insemination somehow having to do with the mechanics or physical artifacts of statement recording, not at all with logic, and so forth and then invert meanings endlessly in the same way two mirrors perpetuate images (nor others who get confused about symmetric operations as opposed to symmetric meaning). As I took it, he meant that from some perspective, one that a particular db was concerned with and only with, one couldn't even mention her name without knowing her telephone number. In a way, this defined all her acquaintances and thus the (imaginary) db concerned with her. Too right, if you ask me, keep the tautologies out of it.

ps:There might be occasional usefulness in making what one might call 'domain assertions', eg., in D&D Algebra, "there is a position called 'toilet scrubber'" could be assessed from R{position} <OR> (<NOT> R{position}) but that must be rare as well as obscure as far as most db discussions are involved.

Another ps is that more and more I think objections to POOD have mostly to do with physical obstacles to do with naming the things we want to record. Received on Mon Sep 27 2010 - 01:11:45 CEST

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