Re: In an RDBMS, what does "Data" mean?
Date: Wed, 16 Jun 2004 14:56:17 GMT
Message-ID: <lcZzc.1825$Pt.1467_at_newssvr19.news.prodigy.com>
"Dawn M. Wolthuis" <dwolt_at_tincat-group.com> wrote in message
news:cal2mk$e5k$1_at_news.netins.net...
> "Eric Kaun" <ekaun_at_yahoo.com> wrote in message
> news:pgkzc.25517$_g6.23406_at_newssvr31.news.prodigy.com...
> > How is this useful? I've seen this in COBOL layouts, and was
underwhelmed;
> > it always seemed to cause more problems (and invite even others) than it
> > appeared to solve. How is this more effective than a view, for example?
>
> Logically that is what it is, I guess, but it can be nested.
>
> Take all of the nouns you want to consider and look at their
relationships.
> Month, Day, and Year are three such nouns and you might want another that
is
> made up of exactly these three -- so you can derive Date as Month | Day |
> Year or derive month, for example, using a function as Month(Date). Now,
if
> you are looking at a list of dates, you can do the same thing, performing
> functions to group or separate various data.
>
> I'm not sure that answered your concern. I think being underwhelmed
> regarding derived data is appropriate in 2004. smiles. --dawn
So I'd set up equivalences like these:
Month(Date(Y, M, D)) = M
Day(Date(Y, M, D)) = D
Year(Date(Y, M, D)) = Y
which assumes only that you have a selector (constructor) Date(Y,M,D). You could set up others, of course, and you'd need domain specifiers over M and Y, and then a constructor for Day that took Month into account.
But I think I've gone far afield of your original points...
- erk