Re: is pivoted phones view updateable?

From: NENASHI, Tegiri <tnmail42_at_gmail.com>
Date: Fri, 17 Nov 2006 19:20:41 +0100 (CET)
Message-ID: <Xns987E87D56F3BEasdgba@194.177.96.26>

"Aloha Kakuikanu" <aloha.kakuikanu_at_yahoo.com> wrote in news:1163785724.105471.177880_at_j44g2000cwa.googlegroups.com:

>
> NENASHI, Tegiri wrote:

>> "Aloha Kakuikanu" <aloha.kakuikanu_at_yahoo.com> wrote in
>> v1 is the view that is a subset of r1: v1 = {1,2,.., 10}.  I removed
>> the attribute name for simplicity.

>
> You made a typo, as clearly you didn't mean v1 = {1,2,.., 10}, or is
> a constant in other words.

I made a typo because before I wrote: v1 = {r1|x = 1..10} instead of v1 = {x in r1|x between 1 and 10}; it is the same like select x from r1 where x between 1 and 10.

> What you meant to say:
>
> v1 = r1 join {1,2,.., 10}

It was a selection, it was not a join.

>

>> >
>> > I agree that this example is not invertible. But switch the roles
>> > of 10 and 100 and it becomes updateable!
>>
>> Please explain.

>
> r1 union {1,2,.., 10} = {1,2,.., 10}

No r1 is the base relation,; r1 = {1..100}; r1 union {1..10} = {1..100} = r1 if union is the set union.

>
> v1 = r1 join {1,2,.., 100}

I do not undestand {1..100}. What is it ? Is it that your database has any relations like the universal set ? It is not practical.

>
> v1 is invertible.

Please do gradually:

1. The database has only r1 = {1..100}
2. The view v1 = {x in r1|x between 1 and 10}
3. Show that v1 is invertible.

If one needs the universal set it is not practical but we can discuss: you must show the implementation of the universal set.

What notation you prefer ? I can use any notation that you like.

--
Tegi



> 

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Received on Fri Nov 17 2006 - 12:20:41 CST