Re: MV Keys


"Jon Heggland" <heggland@xxxxxxxxxxx> wrote in message
news:MPG.1e7e1f4d25e871bb98979e@xxxxxxxxxxxxxxx
In article <1142006381.942511.18190@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
marshall.spight@xxxxxxxxx says...
And just for fun, here's an alternative semantics for the syntax
above, in which the parentheses *do* mean the same thing.

(1,b)

Above, "(" means "introduce a new set, cardinality 1, with
the following attributes."

A set has attributes? No, a set with card 1 has one element. What is
that element? Not "an attributes". :)


A set has at least one attribute, though it can have more. I may be
conflating terminology, but isn't the cardinality of a set an attribute? A
uniform set is a set of something, so wouldn't the type (or domain) of its
elements be an attribute?

{ (1,b), (2,a) }

Here, "{" means "introduce a new set of arbitrary cardinality".
"(1,b)" means the same as it did before, and the comma
after it means "union".

But then you will have a set of set(s), won't you?

Ha!

We are bickering over details again. I believe we now agree sufficiently
on the important stuff.

Sure. I guess what one does in practise, is to use conventional syntax,
and just define the result using such relational terms. I.e. more an
intellectual game than an actual language design / operator
implementation strategy.

That's a bit dismissive, don't you think?

Perhaps. I just don't see this paradigm as very practical, cf. my
examples of how verbose the concrete syntax for it might be (not to
mention strange and unintuitive for the relation-unaware masses). But it
might be like lambda calculus: I wouldn't want to do any actual
programming in it, but it might be useful for theoretical research, or
as a scientific foundation for a system, cf. Date&Darwen's minimal
algebra.

There are some who say UPDATE *is* assignment. :) But are you saying
that you don't have scalar variables, only relvars? Or that you use
UPDATE to change a scalar variable?

Update and assignment are both imperative operators, but they are
not the same thing.

They say update is a special kind/case of assignment, to be more
precise.
--
Jon


.

Relevant Pages

  • Re: MV Keys
    ... and just define the result using such relational terms. ... that you don't have scalar variables, ... Update and assignment are both imperative operators, ...
    (comp.databases.theory)
  • Re: Cantors proof that #(Evens) = #(Naturals) is inconsistent
    ... of cardinality? ... the bijection which you have defined. ... this assignment of values and simultaneously define x_i = ffor all ... f iff is an element of f iff ...
    (sci.math)
  • Ternary Relationship cardinality
    ... I am working on an assignment which has 2 ternary relationship. ... Can someone give me some cardinality examples for N-ary relationships? ... kind of odd to me ...
    (comp.databases.theory)
  • Re: Ternary Relationship cardinality
    ... I am working on an assignment which has 2 ternary relationship. ... Can someone give me some cardinality examples for N-ary relationships? ... kind of odd to me ...
    (comp.databases.theory)