Re: What to call this operator?

From: Jon Heggland <>
Date: Wed, 29 Jun 2005 08:59:47 +0200
Message-ID: <>

In article <>, says...
> > 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.

Minor nit: It would not be infinite if all the domains involved were finite.

> 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?

As fundamental operators. Or to be more precise: projection is called <REMOVE>, specifies the attributes to remove instead of retain, and corresponds to the existential quantifier. I think D&D's <RENAME> could be dispensed with using Tropashko's technique, though.

Received on Wed Jun 29 2005 - 08:59:47 CEST

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