Re: Notions of Type
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Fri, 18 Aug 2006 13:29:53 GMT
Message-ID: <lhjFg.51072$pu3.597341_at_ursa-nb00s0.nbnet.nb.ca>
>>Marshall wrote:
>>
>>>[...]
>>
>>Thanks, and
>>
>>Okay, maybe you are right but what if project is not binary but unary?
>>Isn't the idea of treating it as a binary operator arbitrary? Is it
>>enough to say that a projection joined with the relation it was produced
>>from results in that same relation? Just wondering ...
Date: Fri, 18 Aug 2006 13:29:53 GMT
Message-ID: <lhjFg.51072$pu3.597341_at_ursa-nb00s0.nbnet.nb.ca>
Marshall wrote:
> paul c wrote: >
>>Marshall wrote:
>>
>>>[...]
>>
>>Thanks, and
>>
>>Okay, maybe you are right but what if project is not binary but unary?
>>Isn't the idea of treating it as a binary operator arbitrary? Is it
>>enough to say that a projection joined with the relation it was produced
>>from results in that same relation? Just wondering ...
> > I don't see anything wrong with unary operators. But we can't really > do PROJECT as a unary operator, because we don't have enough > info to know what operators should be left when we're done. (If > we were dealing with binary relations, we could define FIRST > and SECOND, but that's of little use to us here.)
Unless project is not a single operation but a generic powerset of unary operations. Not that I think the idea is necessarily all that useful. Received on Fri Aug 18 2006 - 15:29:53 CEST