Re: storing survey answers of different data types

"paul c" <toledobythesea_at_oohay.ac> wrote in message news:CKiIl.23900$Db2.16726_at_edtnps83...
> Joe Thurbon wrote:
> ...
>> Suffice to say, I was following you until you brought him up. What would
>> Mott's Clamato man think?
>> ...
>
> I guess that television ad' was from so long ago that most people don't
> remember it. An amateur inventor pitches his idea to a Mott's exec, it's
> a device that attaches to the kitchen faucet to dispense the juice. The
> very incisive exec scoffs and asks sarcastically: why stop there? Why not
> just fill the central water supplies with clamato juice? The crackpot
> replies: "boy, you guys really think big!". It often seems to me that the
> db field is so easily stumped by small problems that turn into minor
> crises, eg., the so-called view updating problem has been lingering for
> years now, if it is really a problem it effectively means that Codd's
> model is broken.

It doesn't mean that Codd's model is broken: it means that your interpretation of Date's Principle of Interchangability is just plain wrong. The distinctions between base and derived relvars that limit the kinds of updates that are permissible are neither arbitrary nor unnecessary. An insert into a relvar that is the union of two base relvars is inherently ambiguous, since it implies an insert into at least one but possibly both of the base relvars. Disambiguation is possible, but only through the use of multiple assignment--in fact, Date's Assignment Principle demands the use of multiple assignment. In the same way a delete from a relvar that is the join of two base relvars is inherently ambiguous, since it implies a delete from at least one but possibly both of the base relvars. Again, disambiguation is possible, but only through the use of multiple assignment.

> I think the Mott's exec would have said if the theory doesn't suit the
> purpose, change the theory.
Received on Sat Apr 25 2009 - 05:01:05 CEST