Re: is pivoted phones view updateable?

From: Aloha Kakuikanu <aloha.kakuikanu_at_yahoo.com>
Date: 16 Nov 2006 13:56:25 -0800
Message-ID: <1163714185.566596.267910_at_k70g2000cwa.googlegroups.com>


Aloha Kakuikanu wrote:
> Have you meant
>
> r1(x)
>
> a relation with one argument x, such that domain of x is 1..100? This
> is a constraint:
>
> r1 union {(x=1),(x=2),...,(x=100)} = r1.
>
> Then, what is v1? Perhaps
>
> v1 = r1 join a1
>
> where a1={(x=1),(x=2),...,(x=10)} ?
>
> I agree that this example is not invertible. But switch the roles of 10
> and 100 and it becomes updateable!

In fact the later can be worked out pretty nicely.

We have

A \/ X = A

(e.g. A = {(x=1),(x=2),...,(x=10)})

A \/ B = B

(e.g. A = {(x=1),(x=2),...,(x=100)})

Is

Y = X /\ B

updateable? Clearly:

X >= A >= B

Therefore,

X /\ B = X

! Received on Thu Nov 16 2006 - 22:56:25 CET

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