# Re: more on delete from join

From: Mr. Scott <do_not_reply_at_noone.com>
Date: Mon, 31 Aug 2009 02:52:44 -0400
Message-ID: <fcudnYYzXcqg7gbXnZ2dnUVZ_vOdnZ2d_at_giganews.com>

"Marshall" <marshall.spight_at_gmail.com> wrote in message news:74fe01a5-0682-4831-b3cb-92aac8b42e44_at_t11g2000prh.googlegroups.com... On Aug 30, 7:15 am, "Mr. Scott" <do_not_re..._at_noone.com> wrote:

<snip>

<quote>

> Then why did he bring up solving systems of equations in the
> context of view updates?

Probably because there are many interesting things to learn from considering view updates as being related to solving systems of equations.

</quote>

What things, exactly? I don't see any correlation between view updates and solving systems of equations.

<snip>

<quote>
> For example, an insert into a union
> view involving two tables is not deterministic because there are three
> different combinations of values that could result in the same value for
> the
> view. The system has to guess whether the row must be inserted into one
> table or the other or both. The same can be said of a delete from a join
> view.

That would be one way to do it, but you are the only one talking about doing it that way, and it is, as you say, a poor choice of how to do it.
This is what's called a strawman argument. </quote>

Huh? Are you saying that in a view A(X) union B(X), inserting a row (X=22) into to view is somehow deterministic? How does the system determine whether the row (X=22) goes into A or B or both? The resulting value for the view is the same in any case. How is that a strawman argument?

<quote>
Some systems of equations are overspecified, some are underspecified, and some are uniquely specified. Which one of those do you think might be a good candidate for the kind of view update that would succeed? Would fail?
</quote>

I don't think systems of equations apply to view updates, because view updates involve more than one state of affairs, the state before the update and the state after. Systems of equations are either independent of state or involve one and only one state, so I don't think they are even relevant to the problem of view updates. Received on Mon Aug 31 2009 - 08:52:44 CEST

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