Re: Onto a potential relational manipulation language
Date: Sat, 13 Dec 2008 01:17:34 -0800 (PST)
On 12 déc, 19:58, paul c <toledobythe..._at_oohay.ac> wrote:
> vadim..._at_gmail.com wrote:
> > There is established Logic <-> Algebra correspondence. For
> > propositional calculus we have boolean algebra. What algebra do we
> > have for predicate calculus? None. I'd suggest that RL is predicate
> > calculus without quantifiers and relation attributes.
> > ...
> Hold on, Vadim! Regarding quantification, I thought Codd's algebra
> included analogies for Exists and Forall in the projection (fundamental,
> can't be defined in terms of the other fundamental ops, ie., REMOVE,
> NAND or NOR, and TCLOSE) and division (defineable in terms of the other
> ops). Same must be so of D&D A-algebra. If so, RL must at least have
> quantification since it has a form of projection in its lattice union.
> If I've got all that right, there must be a way to express Forall in RL
> with some syntax or other. Am I distorting the situation?
> (BTW, the thing I like (given my small knowleCone names the attributes
> to be projected and the ones that are 'removed' are implicitly the
> header minus the named ones. But if projection has two operands, it
> opens the door for perhaps more exotic structures, such as the
> "multi-relations" Darwen has written about lately (note I'm not saying
> that he advocates them just because he's written about them), where
> tuples in the same structure can have different attributes. I gather
> part of the motivation behind multi-relations is to help deal with
> so-called "missing information", whereas my attitude so far is that it
> could just as easily be a way for one structure to allow multiple
> predicates, which might give some programming leverage, eg., allowing
> multiple predicate references, even updates in a single structure
Precisely. One can hardly implement a satifactory solution to missing information through decomposition without a computing model that does implement combinatory analysis between domains of un-ary relations that constitute multi attribute relations. I somehow suspect this is orthogonal to the scope of Vadim's remarks. Received on Sat Dec 13 2008 - 10:17:34 CET