Re: A different definition of MINUS, Part 3
Date: Sun, 21 Dec 2008 21:14:59 -0800
Message-ID: <nmF3l.407$wV2.53_at_newsfe07.iad>
vadimtro_at_gmail.com wrote:
...
> Next one may compare D&D <AND>&<OR> based system, with RL join&inner
> union based one in terms of consistency. Both have arguments in their
> favor. D&D system honors distributivity, and De Morgan laws. RL honors
> absorption, so that the subset relation can be generalized to be
> applicable to any pair of relations. Also RL can express projection as
> an (inner) union of a relation with an empty relation. ...
In other words, D&D has absorption when projection is applied and its union allows deMorgan. RL has absorption without projection but projection is defined in terms of a second kind of union. They both have distributivity and associativity and defined identity values although D&D needs only two identities. As for RL and deMorgan, I thought Marshall S said at least a year ago that RL supported deMorgan. I'm not sure, does it? Received on Mon Dec 22 2008 - 06:14:59 CET