Re: Key attributes with list values was Re: What are the differences ...KEY

JOG wrote:
Marshall Spight wrote:
If you want a system that supports identity, you don't want to
be using set theory. There are plenty to choose from, and
they are well-supported and popular!

When I have arbitrary sets of numbers say and I want to use those sets
in some form of manipulation I can, of course, quite happily state them
mathematically something of the nature:

x = {1, 3, 8}, y = {2, 4, 7}, z = {x, y}, etc.

This is simple assignment, and gives my sets a label, or identity if
you will, so that I may go ahead and use these descriptions in future
manipulations without referring to the sets extensionally.

If all you're doing when you say "x = {1, 3, 8}" is declaring
x as an alias for the set, then x has no identity; it is just a
name for the extensional value. This is no different than
if you said "pi = 3.14159". I would call x a "constant",
although it is common parlance to call it a variable,
even if it cannot in any way vary. :-( The = sign would
not properly be called assignement; rather, it would
be called declaration.

If, on the other hand, x is a variable, and supports destructive
update operators, of whatever kind (reassignment, insert,
delete, etc.) then x indeed has identity.


Surely this is identity (an artifice of course, but valuable here
nonetheless) and set theory working in perfect harmony at the heart of
mathematics?

Certainly. Note that the relational algebra has no destructive
update. Insert, delete, etc., are not algebraic operators
but imperative ones. The imperative operators can exist
side-by-side in harmony with the algebraic ones, just like
we can embed the algebra of the integers inside an
imperative language.

However it has occasionally been claimed that individual
rows in a relation have identity. That is, a relation variable
is a set of other variables. This is OOP; it is not relational.
Not that there's anything wrong with that. :-)


Now, this methodology clearly violates the information
principle-centric view of using attributes only to refer to things. Yet
it is exactly the sort of thing I want to do with the data I work with
(genetic and other bioinformatics data), in spite of the cognitive
dissonance it seems to be causing me (yes,trying to reconcile what
currently seem to be equally arguable but opposing standpoints is
hurting my head ).

HTH


Marshall

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