Re: constraints in algebra instead of calculus

From: Jon Heggland <jon.heggland_at_idi.ntnu.no>
Date: Tue, 19 Jun 2007 10:30:01 +0200
Message-ID: <f58469$c6j$1@orkan.itea.ntnu.no>

Vadim Tropashko wrote:
> On Jun 18, 12:15 am, Jon Heggland <jon.heggl..._at_idi.ntnu.no> wrote:

>> I think all this indicates that GROUP is such a difficult operator that
>> using it to express constraints is a bad idea. :)

>
> Grouping is has much in common with set equality join, and set joins
> were are known to be difficult operators:
> http://fie.engrng.pitt.edu/fie2003/papers/1057.pdf

But grouping is also just a particular SUMMARIZE, and SUMMARIZE isn't all that difficult. So I don't really understand what the trouble is.

But I've never bothered to learn relational division properly. :) I've rarely felt the need for it, and using relation comparisons seems much easier.

-- 
Jon

Received on Tue Jun 19 2007 - 03:30:01 CDT