Re: MV Keys

In article <wMUNf.17845$rL5.2737_at_newssvr27.news.prodigy.net>, brian_at_selzer-software.com says...
>
> I don't see it that way. If you can talk intelligently about values that
> are contained in a list apart from that list within the constraints imposed
> by the universe, then the list is not atomic or scalar with respect to the
> universe of discourse. The list can be resolved into components that have
> meaning with respect to the universe independent of the list.

What universe? A concrete example: I can use a varchar as a string (where, for the sake of the argument, I postulate that the individual characters "have no meaning"), or as an array of characters (where they do). The DBMS doesn't know (or care) what meaning I apply to either varchar---so what is the point of the distinction? Just to say that one design (the one using varchar as an array) is probably bad, and the other is not?

My point is that you can't say that a type (e.g. varchar) is scalar or not a priori; you have to say "the way varchar is used by this operation in this particular database means it's not a scalar here". Hence, scalar-ness is a property of some use of some variable of a type, not of the type as such. I think we actually agree; you do say "scalar /with respect to the universe of discourse/" (my emphasis).

> > Speaking of dates, is date a scalar type? Its components (year, month,
> > day) do belong to the universe of discourse in most cases.
>
> Absolutely. Year, month and day are not components, they're
> transformations. Time is a continuum, and dates are points along that
> continuum. Year, month and day are functions of the number of days that
> have passed since a widely accepted point in time.

Or the other way around. Are substrings of strings components or transformations? What about subranges, or individual values, of arrays or lists? What is the difference?

-- 
Jon