Re: Onto a potential relational manipulation language

On 12 déc, 19:58, paul c <toledobythe...@xxxxxxxx> wrote:
vadim...@xxxxxxxxx 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
reference.)
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.
.

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