Re: two nasty schemata, union types and surrogate keys

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.

>> > 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