Re: is pivoted phones view updateable?

From: NENASHI, Tegiri <tnmail42_at_gmail.com>
Date: Sun, 19 Nov 2006 01:28:51 +0100 (CET)
Message-ID: <Xns987FC6A25B28asdgba_at_194.177.96.26>


"Aloha Kakuikanu" <aloha.kakuikanu_at_yahoo.com> wrote in news:1163805202.111347.268880_at_h54g2000cwb.googlegroups.com:

> This example is obvious informally as well. We had an unitary relation
> constrained in {1..10}, we made a view with a "relaxed" constraint
> {1..100}. Clearly it is the same as the base relation!

It is the case of "the dark side of the formalism" like someone said on sci.math: what is apparent very often demands an inconvenient formal language.

>
> The phones example (the one where there were two tables and no NULLs)
>
> X = (Y /\ A) \/ (Z /\ B) -- aka ConsolidatedPhones
>
> is less trivial. Next, there goes an example with join
>
> Y = X join A
>
> subject of constraint
>
> project_y (X(x,y)) is subset of project_y (A(y,z))
>
> which I admittedly failed to work out formally yet (although, I know
> what an inverse view is).

What is it ? I am curious becuase I think that the constraint of the projection does not suffice that the view is updatable.

>
> And, finally, there is a join of relation with function where the joint
> column is projected away. I'm not even sure if relational lattice is
> applicable, as it seems that we need a difference operator...

It is the join on the primary key: the result is non ambiguous. Even Oracle update a view like this ;) The sketch model thinks too it is updatable ;)

>
>
Received on Sun Nov 19 2006 - 01:28:51 CET

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