Re: foundations of relational theory?
Date: Fri, 31 Oct 2003 09:22:12 -0800
Message-ID: <v0xob.18$T3.34_at_news.oracle.com>
"Andrew McAuley" <amcauley_notreally_at_sprezzatura.com> wrote in message news:bnu438$aoj$1_at_sparta.btinternet.com...
> > "Mikito Harakiri" <mikharakiri_at_iahu.com> wrote in message > news:BUvob.16$T3.164_at_news.oracle.com... > > Change equality to inequality. > > > Change from a derived column to a domain level constraint.
Let's restore the context.
<quote>Why would you EVER " have a constraint that an attribute in one
relation
equals a sum of values from another relation."? To do so would be to store
redundant information. I would never dream of doing this as it requires two
updates for every update.
... irrelevant sentence about MV snipped...
Ultimately the same idea as a derived view - a
column that has no value other than that derived by another operation. this
column may be treated to all intents and purposes as a physical
column.</quote>
Should I read the amended quote as
<quote>
Why would you EVER " have a constraint that an attribute in one relation
<my change>greater than</my change> a sum of values from another relation."?
-----------^^^^^^^^^
<invalidated claim>
To do so would be to store
redundant information. I would never dream of doing this as it requires two updates for every update.
</invalidated claim>
... irrelevant sentence about MV snipped...
Ultimately the same idea as a derived view - a
<your change>domain level constraint</your change>
that has no value other than that derived by another operation. this
<your change>domain level constraint</your change>
may be treated to all intents and purposes as a physical column.</quote>
Did I made substitution correctly? I don't think I'm able to make any sence out of the second part telling something about domain level constraints. Received on Fri Oct 31 2003 - 18:22:12 CET