Re: Database design, Keys and some other things

-CELKO- wrote:
> >> Consider you have a car and over 20 years you gradually bit by bit change
> >> every single part of it. The paint job, the engine, the interior, the
> >> chassis... everything, bit by bit. After 20 years it doesn't have a single
> >> component that was originally in it. It is still the SAME car?
>
> This is the problem of King Somebody's Charriot from Budhist literature.
> The auto industry solved it by saying that a car is the engine block with the
> VIN number stamped into it. Everything else is an add-on.

Great example. King Milindi's chariot - a bhuddist philosopher used it
as an argument against essentialism, to illustrate that there is no one
attribute of an item that can define its essense.

The monk might say to you that the VIN is a great identifier until the
car is stolen (this happens a lot in my neighbourhood), and the thieves
cleave off the VIN and repaint it. It would still be my ruddy car they
were driving around in (despite what philosophers like Leibniz would
probably tell me).

Primary keys are supposed to be immutable. RM relies on this for smooth
running, preventing dangling references and isolated records. But given
that in reality no primary key, or combination, can be gauranteed to be
so, and no natural keys can represent an entity's "essence", every
predicate is a King Milindi Chariot. Course, this doesn't stop us
having usable database admin's handle it with good old common sense,
but imo it's certainly not a rock solid foundation for the theory.

.

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