Re: more on delete from join
Date: Wed, 26 Aug 2009 11:18:05 -0700 (PDT)
On Aug 26, 10:40 am, paul c <toledobythe..._at_oohay.ac> wrote:
> Insert to a base relvar represents a conclusion: R =: R UNION A conludes
> R AND A.
What is "R AND A"? Some proposition (aka 0-ary predicate)? This can't be because join of R and A certainly is not 0-ary.
According to D&D the <AND> is an operator which applied to relations produces a relation. Therefore, in order to make a logical interpretation one have to associate some relations with true and false propositions. DEE and DUM are obvious candidates on this.
The <AND>,<OR>, and <NOT> operators prompt boolean algebra analogy. However, even though algebra of relations has similar operators to boolean algebra, it is quite distinct from boolean algebra. How different they are? Relational lattices answer to that question (among other things). Received on Wed Aug 26 2009 - 20:18:05 CEST