Re: A different definition of MINUS, Part 3
From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Sun, 21 Dec 2008 20:13:12 -0400
Message-ID: <494edb9a$0$5477$9a566e8b_at_news.aliant.net>
>
> Two reasons:
> 1. Relational Algebra is a weaker system than boolean algebra.
> Therefore there is no reason to expect BA properties to carry over.
> 2. All RA operation, not just three can be reduced to a single one.
> Here is my worksheet:
>
> Join, is <AND>. It is representable in terms of Sheffer stroke.
> Projection, is inner union in RL terms. Well, I don't see how to
> represent inner union in terms of other operations:-(
Date: Sun, 21 Dec 2008 20:13:12 -0400
Message-ID: <494edb9a$0$5477$9a566e8b_at_news.aliant.net>
> On Dec 21, 11:53 am, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
>
>>vadim..._at_gmail.com wrote: >> >>>On Dec 21, 11:36 am, vadim..._at_gmail.com wrote: >> >>>>x + y = ((x ^ x)' ^ (y ^ y)')'. >>>>... is tough... >> >>>Actually, easy. The right side simplifies to >> >>>x + y = (x' ^ y')'. >> >>>Applying double negation (provable in RL), we get >> >>>(x+y)' = x' ^ y'. >> >>>De Morgan, which is again provable in RL. Amazing. >> >>Why are you amazed?
>
> Two reasons:
> 1. Relational Algebra is a weaker system than boolean algebra.
> Therefore there is no reason to expect BA properties to carry over.
> 2. All RA operation, not just three can be reduced to a single one.
> Here is my worksheet:
>
> Join, is <AND>. It is representable in terms of Sheffer stroke.
> Projection, is inner union in RL terms. Well, I don't see how to
> represent inner union in terms of other operations:-(
Sigh. One of these days, I really do have to take the time to better understand the RL. Projection, to me, doesn't seem like any sort of union. Received on Mon Dec 22 2008 - 01:13:12 CET