Re: A pk is *both* a physical and a logical object.

From: Bob Badour <>
Date: Tue, 14 Aug 2007 13:25:34 -0300
Message-ID: <46c1d740$0$4056$>

JOG wrote:

> On Aug 13, 7:27 pm, "Brian Selzer" <> wrote:

>>"JOG" <> wrote in message
>>>On Aug 13, 6:56 am, "Brian Selzer" <> wrote:
>>>>"JOG" <> wrote in message
>>>>>On Aug 5, 3:26 pm, "Brian Selzer" <> wrote:
>>>>>>"JOG" <> wrote in message
>>>>>>>Just as another example of what i'm on about with this construct
>>>>>>>m'larkey: Imagine the library has two copies of "harry potter and
>>>>>>>deathly hallows". Are they the same book?
>>>>>>>1) If your construct is the one that uses the barcode on the sleeve
>>>>>>>an identifier, then no, different books.
>>>>>>>2) If your construct is the one that uses the ISBN number as an
>>>>>>>identifier, then yes, same book.
>>>>>>>There's no correct answer, and which you pick just depends on the
>>>>>>>application. A Loans database could use Barcodes; A library listings
>>>>>>>database could use ISBN.
>>>>>>A very thought-provoking example.  Are they the same book?  From the
>>>>>>information given, no, they're not the same book.  They are two
>>>>>>physical manifestations of the same abstract individual.  Abstract
>>>>>>individuals are incomplete in the sense that they cannot exist apart
>>>>>>their physical manifestations, for to exist is to be spatiotemporally
>>>>>>As a consequence, the identity relation fails just in case there
>>>>>>are no physical manifestations; therefore, it must be assumed that
>>>>>>exist physical manifestations.  So if each tuple in a relation
>>>>>>specific abstract individual, then that relation must be a projection
>>>>>>another--even if it isn't defined in the schema.  Since the abstract
>>>>>>individual exemplifies all of its physical manifestations and cannot
>>>>>>apart from those physical manifestations, the existence of a tuple in
>>>>>>relation that uses ISBNs as key values implies the existence of at
>>>>>>tuple in a relation that uses barcodes as key values--even if the
>>>>>>relation is not defined in the schema.  If at some point in the future
>>>>>>loans and library listings databases were combined, there would
>>>>>>be a
>>>>>>cyclical relationship between the set of abstract individuals denoted
>>>>>>ISBNs and the set of concrete individuals denoted by barcodes.
>>>>>I'm glad you thought it was an interesting example. I personally see
>>>>>no distinction between your "abstract" and "physical manifestations".
>>>>>To illustrate this all i'm asking is that you just extend the example
>>>>>to use more constructs - maybe I now have five books, the two harry
>>>>>potters from before,  another that's got illustrations, one translated
>>>>>into mandarin and a digital version.  We now have an almighty
>>>>>conundrum if someone asks us "which of these are the same book". How
>>>>>do you split up "physical" and "abstract" now? It would be an absolute
>>>>>spaghetti to try to hazard an answer!
>>>>It is simple.  An abstract individual cannot be spatiotemporally located.
>>>>The one thing that the five individuals above have in common is the
>>>>individual: they are all physical manifestations of it.  Neither the
>>>>addition of illustrations, the translation into mandarin nor the encoding
>>>>into digital form changes the fact that the abstract individual
>>>>each of those five tangible instances.
>>>Nope, you've missed the point. There are now several possible
>>>'abstract' individuals. There are now also about a dozen ways of
>>>answering the question "which of these books are the same". Have a
>>>look at the different possible answers.
>>I may be dense, but you're right, I've missed your point.  There is only one
>>abstract individual that exemplifies all of the concrete instances.  There
>>may be additional abstract individuals, such as the set of illustrations, or
>>the translation.  Is that your point?

> Yes, pretty much. Lots of possible constructs. Which of the books are
> the same?
> 1) All - all harry potter and the deathly hallows (identifying
> attribue for a "book" - title)
> 2) None - all the copies are different (identifying attribute for a
> "book" - barcode)
> 3) The two paperpack versions (identifying attribute for a "book" -
> isbn)
> 4) All the english versions (identifying attribute for a "book" - its
> content)
> 5) All the english versions without illustrations (identifying
> attribute for a "book" - its text)
> 6) etc, etc...
> All are valid answers. No context to the question - no suitable
> answer. Pick the wrong one for the context you need, broken schema.
> Here we are comparing different items, but we could just as easily be
> comparing the things at different points in time. Something is only
> the same entity if /for the context we chose/ its identifying
> attribute is the same - all of its other properties may change, but if
> the identifying attribute changes then it is a different thing as far
> as that context is concerned.
> Again let me emphasize that this is all at the conceptual level. But
> it is only when one has that level sorted that one can move down to
> the logical encoding.

If you are not careful, Marvin Minsky will show up to explain frames. Received on Tue Aug 14 2007 - 18:25:34 CEST

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