Date: Tue, 08 Jul 2008 17:35:24 GMT
Brian Selzer wrote:
> "Bob Badour" <bbadour_at_pei.sympatico.ca> wrote in message
>> paul c wrote: >> >>> Brian Selzer wrote: >>> >>>> "paul c" <toledobysea_at_ac.ooyah> wrote in message >>> ... >>> >>>>> However, I'm content to say that all three relations have the same >>>>> predicate, assuming no attribute renaming is involved in your >>>>> interpretation. I know many people say that the 'or' is introduced to >>>>> the predicate of R. I don't believe there is any law or principle, >>>>> including relational closure, that requires anybody to think this way. >>>>> >>>> How can they have the same predicate if they can have different >>>> extensions? That doesn't make any sense. >>>> ... >>> They are misconceived. The example strikes me as akin to Joe C's word >>> games. >> To answer Selzer's query, they have different external predicates but the >> same predicate as far as the DBMS can calculate.
> That doesn't make sense either. If there are different external predicates,
> then shouldn't that be reflected by there being different relation names,
> and thus differing internal predicates?
(Surely relation names aren't anything but an implementation device.) Received on Tue Jul 08 2008 - 19:35:24 CEST