Re: Which normal form is this violating?

From: Paul Vernon <paul_vernon_at_ukk.ibmm.comm>
Date: Sun, 12 May 2002 13:41:38 +0000 (UTC)
Message-ID: <ablrei$a8e$>

> The reason that you had to compare the two tables is because you
> didn't know whether they represented the same predicate or not. Keep
> in mind that the database cannot in general know if two tables are
> logically the same or not.

So, if I have two tables with the same predicate (which, if I followed the thread correctly we *are* allowed - albeit in contradiction to Date's principle of Orthogonal Design), then if I rename the first table to be the same as the second, should a good DBMS in fact merge the two tables into one / return an error if the two tables state any contradictory facts ? Sound like a neat feature to me.

But then again, what about a view that was a union of the two tables? Would I receive a run time error if the tables ever came to state contradictory facts, or would the view creation have a side effect of constraining the tables to not get in such a state?

All sort of interesting in data integration scenarios and makes me wonder about what role 'names' have in the Model. I.e. I question Date's statement that "encoding meaning into names - of relvars or anything else - violates the Information Principle". My answer being, well what is in the system catalog if not names of relvars, attributes and types?

Paul Vernon Received on Sun May 12 2002 - 15:41:38 CEST

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