Re: Is mysql a RDBMS ?

"Leandro Guimarães Faria Corsetti Dutra" <lgcdutra_at_terra.com.br> wrote in message news:pan.2003.08.27.12.27.34.16318_at_terra.com.br...
> On Mon, 25 Aug 2003 18:55:13 +0000, Anith Sen wrote:
>
> >> As if view updates problem is solved in the pure relational theory. <<
> >
> > Who said so? This is exactly what I mentioned as being explored & lack
of
> > well-defined theoretical basis.
>
> AFAIU, D&D have actually provided a nice updateability model in _TTM_...

No. Any practical implementation of relational model must admit functional operators. Math operators including: sin, exp, ln, etc. And with operators view updates is just insanely complex. Simple example:

select Radius*sin(Angle) as Y, Radius*cos(Angle) as X from PolarPoint

is perfectly updateable view, but the RDBMS must be aware of a lot of math to be able to invert it. Well in this example the math is trivial

select X*X+Y*Y as Radius, arctan(Y/X) as Angle from CartesianPoint

but it easily becomes graduate level math when column expressions are polynomials. And those are special cases only!

As you see almost none of the relational operators is used in that view (no join, no union, no restrict), so you simply have no way to leverage D&D ad-hock updateability rules. Received on Wed Aug 27 2003 - 18:18:02 CEST