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

"Roy Hann" <specially_at_processed.almost.meat> wrote in message news:T-ednd6X0L5qsAPbnZ2dnUVZ8rOdnZ2d_at_pipex.net...
> "Bob Badour" <bbadour_at_pei.sympatico.ca> wrote in message
> news:469e067b$0$8844$9a566e8b_at_news.aliant.net...
>> Roy Hann wrote:
>> Unless we are doing a simulation. In which case, we seek to manipulate
>> in the safe knowledge that we end up with a representation of what we
>> think the real world would have been had it started with the same
>> boundary conditions.
>
> Fair enough, and the practical example would be when we are running
> through a test script.
>
>> The truth of the matter is worlds are meaningless to mathematical
>> abstractions.
>
> I'll take your word for it. But surely we are interested in a lot more
> than mere abstraction here? We are interested in finding *just* those
> abstractions whose behaviour is a good analogue to the real world. Or to
> put it differently, we are interested in how set theory and predicate
> logic can be *applied* to real world data management. It's the
> "applied-ness" that makes all the difference, and there is only one world
> where anything can be applied.
>
> Brian's assertion that some arbitrary update can cause a possible world to
> become an actual world is like something out of Gulliver's Travels.
>

The schema of a database describes a set of possible database values, each of which represents a complete description of a situation that may occur, and the body of a database, the actual database value, represents a complete description of the situation that is actually occuring. In this context, a world is a situation, an instance of the universe--a particular set of circumstances that can or do obtain. An update clearly designates which of the possible database values is now the actual database value, and since there is a bijective mapping between the set of all possible database values and the set of all possible worlds, it stands to reason that an update causes a possible world to become the actual world.

> Roy
>
Received on Thu Jul 19 2007 - 12:56:15 CEST