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Home -> Community -> Usenet -> comp.databases.theory -> Re: A pk is *both* a physical and a logical object.

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

From: David Cressey <cressey73_at_verizon.net>
Date: Thu, 19 Jul 2007 11:28:07 GMT
Message-ID: <bVHni.12870$s25.12266@trndny04>

"Brian Selzer" <brian_at_selzer-software.com> wrote in message news:jrHni.23333$Rw1.18184_at_newssvr25.news.prodigy.net...
>
> "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.

In the databases I have worked on, the cause and effect is reversed from what you said above. It's a change of state of the actual world that causes an update to be made to the database.

This process is not perfect, because it depends on the state of knowledge of those empowered to update the database, and also on them carrying out their assigned role regarding database updates. Received on Thu Jul 19 2007 - 06:28:07 CDT

Original text of this message

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