Re: MV Keys

"Jon Heggland" <heggland_at_idi.ntnu.no> wrote in message news:MPG.1e7e1f4d25e871bb98979e_at_news.ntnu.no...
> In article <1142006381.942511.18190_at_v46g2000cwv.googlegroups.com>,
> marshall.spight_at_gmail.com 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
Received on Sun Mar 12 2006 - 13:35:49 CET