Re: What to call this operator?

paul c wrote:
> D&D chapter 4 intrigues me for a similar reason - it seems more directly
> programmable suggesting a more elemental (and i would hope, smaller)
> implementation without the confusion that i think the sql products have
> produced with their attention to user artifacts such as files and
> 'tables' which seem to have led to all kinds of detours and dead ends
> over the last 30 years. just my intuition too.

SQL products aside, 5 basic classic relational operators (+renaming) is just too many for an algebra to bear. And then, when we consider view equations, an algebra with complex operators simply defy developing any expression rewriting technique.

> the place of <OR> in the world puzzles me too. for one thing it appears
> to me that it produces the same result of <AND> when there are no
> attributes in common, ie. cartesian product. am i wrong?

If relations have disjoint headers, the result would be an infinite relation, not the Cartesian product.

> if it does product the cartesian product, is this somehow contrary to
> orthogonality?
>
> so far, the only use i can see for <OR> is as a separate version to
> double-check the results of <AND> and <NOT>. or maybe as an
> optimization on occasion.

Once again, there are at least three versions of union definition to consider:

1. D&D
2. outer union
3. Lattice

I don't quite see though how options #1 and #2 help reducing the number of primitive operations. How does D&D represents renaming and projection, for example? Received on Tue Jun 28 2005 - 22:48:41 CEST