Re: I am looking for references on updatable views

Mikito Harakiri wrote:
> "Show me your view update strategy, and I'll prove it failing on my
> example"
>
> The example I have in mind is very simple. Consider
>
> rename( X(t,v), v->w ) = Y(t,w)
>
> If we update the view Y, what modification to the relation X data
> should be? This might seem absurdly naive example, since the view
> equation solves in a moment
>
> X(t,v) = rename( Y(t,w), w->v )
>
> Not so fast, however. Let <v=w> be (an infinite) binary relation
> {(v,w) | v=w}. Then, the first view equation can be written as
>
> project_t_w(X(t,v) join <v=w>) = Y(t,w)
>
> Y is still a perfectly updateable view, but suddenly, the method of
> solving this equation becomes not obvious.

Interesting.

I like to think of joins with infinite relations as rather being joins with intentional relations, aka functions. That is, rather than joining with {(v,w) | v=w}, we instead join with func(v -> w) { w = v; }

In such cases, being able to apply the reverse of the join requires being able to invert the function. Since assignment is invertible, this would seem to work okay.

Marshall Received on Sat Oct 08 2005 - 05:48:01 CEST