Re: A question for Mr. Celko

"Jan Hidders" <jan.hidders_at_REMOVETHIS.pandora.be> wrote in message news:pan.2004.07.19.09.47.05.758730_at_REMOVETHIS.pandora.be...
> On Mon, 19 Jul 2004 02:41:36 +0000, Marshall Spight wrote:
> >
> > In light of this view, I don't see anything in Date's interpretation
> > of 1NF that means that values aren't atomic anymore. On the
> > other hand, I could imagine you describing this interpretation
> > of "atomic" as trivializing the concept of atomicity as well,
> > which it kind of is.
>
> No no, that's not the problem, or at least not what I think is the
> problem. Date allows the NEST and UNNEST operations from the nested
> relational algebra. (He calls them GROUP and UNGROUP for some reason.)
> That means that you no longer consider them atomic because they allow you
> to split a nested relation into its constituent parts.

I guess I'm still not clear on what you mean. If we can take the value out of a variable and produce "sub-values" out of that, then I don't see any problem with that. Just like taking the third character in a string, or bit-5 out of an int.

If we can perform an update on some subcomponent of a relation variable, then I still don't see a problem. UPDATE Table set attr = 5 where id = 6.

If, on the other hard, we can create a new variable that is itself a "subvariable" of another variable, and have updates to one affect the other, then you've got an aliasing problem, although I'm still not clear on how bad that is in practice.

Perhaps I should just stop asking naive questions and go read about nested relational algebra.

Marshall Received on Mon Jul 19 2004 - 15:59:35 CEST