Re: views of binary operations
Date: 17 Jul 2006 05:08:01 -0700
Message-ID: <1153138081.725088.171520_at_m79g2000cwm.googlegroups.com>
erk wrote:
> Cimode wrote:
> > Aloha Kakuikanu wrote:
> > > Marshall wrote:
> > > > Aloha Kakuikanu wrote:
> > > > > Marshall wrote:
> > > > > > Consider named views of binary operations on relations.
> > > > > >
> > > > > > Given a relational operator "op" and relation variables A and B,
> > > > > > and a declaration of:
> > > > > >
> > > > > > r = A op B
> > > > > >
> > > > > > the language evaluates the expression "A op B" and assigns the
> > > > > > result to r.
> > > > > >
> > > > > > However, if we declare this as a view, ...
> > > > >
> > > > > View is a named expression. r is a view.
> > > >
> > > > Is it necessarily named? Might we find use for an anonymous view?
> > >
> > > Well, the point is that the term "view" is redundant and SQL-ish.
> > > Relations and relational expressions are the fundamental concepts, and
> > > view is some bastardized idea.
> > I agree. I would go one step further to deal with Marshall's question
> > not use the term *view* at all. As I have said, anything related to
> > SQL is one way or another a source of confusion when dealing with RM
> > issues.
>
> Views and snapshots aren't unique to SQL. They're fundamental to
> relational.
I understand and agree but views and snapshots are not *always* necessary to understand RM issues. Marshall's question seems to directly point out directly to inter relation assignment rather than views or snapshots.
> A simple rule of thumb might be this: A view is an expression,
> unevaluated, while an assignment necessarily requires a value, thus a
> snapshot. Special syntax is needed to differentiate a view creation
> ("view(r) = A op B" or perhaps "view r = A op B") from a simple
> assignment of a relval to a relvar ("r = A op B").
As stated previously, I am not convinced that r = A op B can not
logically lead to view(r) = A op B because it supposes r = view(r)
which is a shorcut leading to an absurdity which is that a relation is
the same as a view defined on the relation. OTOH view(r) = view(A op
B) would be acceptable.
Received on Mon Jul 17 2006 - 14:08:01 CEST