Re: A pk is *both* a physical and a logical object.
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Wed, 15 Aug 2007 09:43:31 -0300
Message-ID: <46c2f4b4$0$4056$9a566e8b_at_news.aliant.net>
>
>
> Nice little example. The answer is that in your schema you have no
> concept of a computer. None whatsoever. A computer does not exist.
> There is just a relationship between several components. A computer
> (which you have defined as a set of components) has no identity of its
> own over time outside the things it contains - and as such, if these
> components can be changed, it simply cannot be identified throughout
> its lifetime.
>
> Hence if you switch a component, well then you have a different set of
> components. And if you want to call that set of components a computer,
> yes, you have a different computer.
>
> If this was not what was desired (as I imagine) then your schema was
> broken. Your computer should have an id on the box to allow it to be
> identified / give it an identity.
>
> Make sense?
>
>
>
>
> "identity is that set of properties that defines the individual." -
> what does that mean, if not the properties that distinguish it from
> other entities of the same type in that universe?
>
>
>
>
> If /noone/ can identify it any longer you still think the original can
> has some god-given soul-number? Us, humans, give something an identity
> - it doesn't just exist as a force of nature.
>
>
>
>
> An update replaces a relation with a new one with a delete, and then
> replaces it again with another new relation with an insert. Just
> because it the system does some jiggery pokery to work out which
> proposition to delete, and the content of the new one to be inserted
> does not change this.
>
>
>
>
> In that (let us note different) situation there would be two different
> definitions of the relative identity of a can. One would be its point
> in space (which one observer has tracked) and the other its no. ID,
> which someone else is observing. Two different constructs. Neither is
> right, neither is wrong. Two things with their own distinct identity.
>
> And given I'm sure your not suggesting that someone should walk around
> pointing at things continually to give them their identity, they must
> have an observable property that does not change in the propositions
> in which they feature, otherwise they simply could not be recognized
> as the same thing in real life, never mind a database encoding.
>
> I know this is a subtle, uncomfortable way of viewing things - but
> I've managed to shake off the idea that something has an identity even
> if noone is observing it, so I'm sure others can. There is nothing to
> relative identity outside an objective human decision. Recognizing
> this means good conceptual modelling, as making the right decision is
> down to us. Regards, J.
>
>
Date: Wed, 15 Aug 2007 09:43:31 -0300
Message-ID: <46c2f4b4$0$4056$9a566e8b_at_news.aliant.net>
JOG wrote:
> On Aug 15, 6:45 am, "Brian Selzer" <br..._at_selzer-software.com> wrote:
> [snip]
>
>>A simple example: Suppose that you built several identical computers. Each >>has one motherboard, one DIMM, one hard drive, one video board, and one >>case. Each component is serialized, so the serial number for each component >>would be a candidate key value in a relation describing the composition of >>each computer. You're having trouble with one of the computers, but you're >>not sure which component is failing, or even if it is a hardware problem, so >>you swap the hard drives from two of the computers to see if the problem >>moves. For either of the two computers affected by the swap, the >>motherboard is the same, the DIMM is the same, the video board is the same, >>and the case is the same. So obviously, since those serial numbers are the >>same before and after the swap, it's the same computer, right? But wait, >>the hard drive is different; therefore, it must not be the same computer >>because the serial numbers for the hard drives are different.
>
>
> Nice little example. The answer is that in your schema you have no
> concept of a computer. None whatsoever. A computer does not exist.
> There is just a relationship between several components. A computer
> (which you have defined as a set of components) has no identity of its
> own over time outside the things it contains - and as such, if these
> components can be changed, it simply cannot be identified throughout
> its lifetime.
>
> Hence if you switch a component, well then you have a different set of
> components. And if you want to call that set of components a computer,
> yes, you have a different computer.
>
> If this was not what was desired (as I imagine) then your schema was
> broken. Your computer should have an id on the box to allow it to be
> identified / give it an identity.
>
> Make sense?
>
>
>>[snip] >> >>>>In addition, identification is not identity! >> >>>Aha! That's where we differ then. That is /exactly/ what identity is >>>in my opinion. Identification is stating that if I know one attribute >>>(or set of attributes) I can functionally determine the rest. Perhaps >>>we should discuss that and then the rest of the arguments might fall >>>into place? Let me start the ball rolling, with a catfood example for >>>the new century ;) >> >>An individual's identification is a set of properties that distinguishes the >>individual from all others in the context of a picture of the universe; an >>individual's identity is that set of properties that defines the individual. >>These are two different things.
>
>
> "identity is that set of properties that defines the individual." -
> what does that mean, if not the properties that distinguish it from
> other entities of the same type in that universe?
>
>
>>>------------------------------------------ >>>I am shown a can of catfood from an identical batch of three. Its >>>only, single identifying feature is a number on it. I read it, and the >>>can is taken away. I am then shown a new can. Is it the same can? Does >>>it have the same identity? I read the number on it, which is >>>different. I conclude therefore, quite sensibly, it is a different can >>>to the first. >> >>>Unbeknownst to me someone had shuffled the can numbers up at random >>>after i'd read the first one. Even this mischevious soul himself has >>>no idea if the original can I was given ended up with the same number >>>on it as before (the shuffling was done blind). In fact /noone/ in the >>>world now knows. >> >>>Where does identity stand now? >>>------------------------------------------ >> >>Identity stands as it always did. What is different is identification.
>
>
> If /noone/ can identify it any longer you still think the original can
> has some god-given soul-number? Us, humans, give something an identity
> - it doesn't just exist as a force of nature.
>
>
>>This is a perfect example of why update is primitive and assignment isn't. >>An assignment replaces the current relation value with a new one, blindly, >>but an update specifies which tuples are different and how each differs,
>
>
> An update replaces a relation with a new one with a delete, and then
> replaces it again with another new relation with an insert. Just
> because it the system does some jiggery pokery to work out which
> proposition to delete, and the content of the new one to be inserted
> does not change this.
>
>
>>which has the same effect as observing each can of cat food throughout the >>interval from the first reading to the second. Obviously, if you were able >>to simultaneously observe each can, then there would be no doubt as to >>whether the new can is the original can.
>
>
> In that (let us note different) situation there would be two different
> definitions of the relative identity of a can. One would be its point
> in space (which one observer has tracked) and the other its no. ID,
> which someone else is observing. Two different constructs. Neither is
> right, neither is wrong. Two things with their own distinct identity.
>
> And given I'm sure your not suggesting that someone should walk around
> pointing at things continually to give them their identity, they must
> have an observable property that does not change in the propositions
> in which they feature, otherwise they simply could not be recognized
> as the same thing in real life, never mind a database encoding.
>
> I know this is a subtle, uncomfortable way of viewing things - but
> I've managed to shake off the idea that something has an identity even
> if noone is observing it, so I'm sure others can. There is nothing to
> relative identity outside an objective human decision. Recognizing
> this means good conceptual modelling, as making the right decision is
> down to us. Regards, J.
>
>
>>>>Identification is used by one individual to pick another out of a crowd, >>>>whereas identity is what one individual is. It may be that much of the >>>>confusion is caused by misinterpreting this simple distinction. >>>>Identification is the nominative form of the verb "to identify." >> >>>>Update is a primitive operation. It is not a shortcut--it cannot be a >>>>shortcut, because not all key values permanently identify individuals.
Jim, why do you continue to elevate this guy? I suggest cutting him off, and I don't care whether you use Occam's Razor or Grampa's axe to do it! Received on Wed Aug 15 2007 - 14:43:31 CEST