Re: two nasty schemata, union types and surrogate keys

On Oct 21, 7:25 pm, r..._at_raampje.lan (Reinier Post) wrote:
> Brian wrote:
> >On Oct 20, 3:18 pm, rp..._at_pcwin518.campus.tue.nl (rpost) wrote:
> >> Brian wrote:
> >> >Under the closed world intepretation, every formula that can be
> >> >represented in a table is assigned a truth value--positive for those
> >> >that are actually represented in the table and negative for those that
> >> >aren't, but under the open world interpretation, only those that are
> >> >actually represented are assigned truth values.
>
> Yes.  Thus far I agree.
>
> >> Let's put it another
> >> >way: either it is supposed to be true or it is known to be true.
>
> ??
>
> >> >Under the closed world interpretation, what is represented is supposed
> >> >to be true, but under the open world interpretation, what is
> >> >represented is known to be true.
>
> ???  No. Under both representations, the tuples in a relation represent
> statements supposed to be true.  The difference regards only the tuples
> *not* in the relation: under the CWA, these correspond to statements
> supposed to be false, while under the OWA they may just as well be false.

Under the open world interpretation, tuples that can be in a relation but aren't represent propositions that may or may not be true. In other words, it is unknown whether those propositions are true or false, but for the tuples that are in a relation, it is not unknown whether the propositions represented are true because they are in fact supposed to be true. It follows, therefore, since it is not unknown whether the propositions represented are true, that they are known to be true.

>
> >> > Bottom line: it would be pointless
> >> >to suppose that what is represented is known to be true.
>
> I have no idea what you mean to say here.
>
> >Under the closed world interpretation, only and all true propositions
> >are represented as tuples in the relation; under the open world
> >interpretation, only but not necessarily all true propositions are
> >represented as tuples in the relation.
>
> Exactly.
>
> >In other words, under the
> >closed world interpretation, what is represented is supposed to be
> >true, but under the open world interpretation, what is represented is
> >only what is known to be true.
>
> There is a deep misunderstanding here.  I can't figure out what it is.
>
> --
> Reinier
Received on Fri Oct 23 2009 - 05:54:18 CEST