Re: two nasty schemata, union types and surrogate keys
Date: 31 Oct 2009 12:36:35 GMT
>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.
They are supposed to be true, not known to be true. A database relation cannot be guaranteed to express facts, It expresses statements of fact, given an interpretation as a predicate. Whether this interpretation follows CWA or not doesn't make a difference.
>It follows, therefore, since it is not unknown
>whether the propositions represented are true, that they are known to
But this is no different from the tuples in a relation interpreted under the closed world assumption.
>> >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.
I still don't understand what difference between 'supposed' and 'known' you have in mind here.
-- ReinierReceived on Sat Oct 31 2009 - 13:36:35 CET