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

"Roy Hann" <specially_at_processed.almost.meat> wrote in message news:BI2dnYRWNeP4VADb4p2dnAA_at_pipex.net...

> "Brian Selzer" <brian_at_selzer-software.com> wrote in message 
> news:oXdni.23174$Rw1.4623_at_newssvr25.news.prodigy.net...
> [snip]


>>> You can call what the user issued an update, if you care to,  but what


>>> really happened is that an individual,  identified by the before value 

>>> of

>>> the key,  was deleted,  and a new individual, identified by the after 

>>> value

>>> of the key was inserted.  The fact that the old value and the new value 

>>> used

>>> the same storage  ("row", if you like)  is irrelevant.  They are 

>
> What is the so-called "individual" here?  The widget, the lot number or 
> the location?    You've told us the key is the entire header, so it is 
> irreducible, so none of these is inescapably unique in this table.
>

The widgit.

>> Now assuming that there can only be one widgit from the same lot at a
>> particular location, then the definite description before the update,
>>
>> the widgit with lot number 203 at location 22
>>
>> refers to the same widgit as the definite description after the update,
>>
>> the widgit with lot number 203 at location 44.
>>
>> If there is also a rigid designator, then the situation becomes clear:
>>
>> before the update, these all denote the same individual:
>>
>> the widgit with serial number 123 and with lot number 203 at location 22
>> the widgit with serial number 123
>> the widgit with lot number 203 at location 22
>>
>> which is the same individual as these:
>>
>> the widget with serial number 123 and with lot number 203 at location 44
>> the widget with serial number 123
>> the widget with lot number 203 at location 44
>>
>> after the update.
>>
>> So, if relation widgits {lot_number, location}
>> has a tuple {lot_number=203, location=22}

>
> How the heck does this tuple represent *anything* about widget 123 (or any 
> other particular widget) if the serial number isn't an attribute?   The 
> only way it can do that is if you first assert your entire relation 
> represents propositions about the widget with serial number 123 
> exclusively.  That's fair enough and I'd have no problem with it, but you 
> aren't saying that.
>

It doesn't. I introduced serial number to illustrate the point that the same individual can exist at different possible worlds even if its definite description is not rigid. At this point that point had already been made. What followed ties that fact back to databases.

{lot_number, location} is the key for widgits. (Again, there can only be one widgit with the same lot number at a particular location.) So {lot_number=203, location=22} identifies a particular widgit at a given database value.

>> and an update is issued:
>>
>> UPDATE widgits SET location=44 WHERE lot_number = 203 AND location=22
>>
>> Then the resulting relation has a tuple
>>
>> {lot_number=203, location=44}
>>
>> that refers to the same individual as the tuple
>>
>> {lot_number=203, location=22}
>>
>> before the update.

>
> I am now satisified that you are talking nonsense.  Erudite-sounding 
> nonsense but still nonsense.
>
> Roy
>