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Home -> Community -> Usenet -> comp.databases.theory -> Re: curiousity of sets of no relations?
Bob Badour wrote:
> P.S. Table_Dee is not a valid result for Intersection because
> intersection is defined on specific types of relations and not on
> general relations the way Join is defined. A universal relation on RT is
> not a valid result for Join because Join is not defined on a specific
> type the way Intersection is.
I'm easily confused when I try to compare the two, maybe because of thinking that the set of all possible intersections is a subset of all possible joins. Red herring maybe due to introducing def'ns of competing operators, same phenomenon that makes contract law such a mess.
(one practical reason i like this "universal" relation, maybe it's the same reason I like <OR> and <NOT> in TTM is that it is a 'defined' way to produce the extension of a domain that is faster than typing it in!)
p Received on Sat Jun 10 2006 - 11:58:27 CDT