# Re: A simple notation, again

From: David Cressey <cressey73_at_verizon.net>
Date: Tue, 17 Jul 2007 07:16:12 GMT
Message-ID: <01_mi.3903\$Gx5.1898_at_trndny02>

"Brian Selzer" <brian_at_selzer-software.com> wrote in message news:OrOmi.22180\$RX.13107_at_newssvr11.news.prodigy.net...
>
> "David Cressey" <cressey73_at_verizon.net> wrote in message
> news:o4Lmi.4051\$fj5.2089_at_trnddc08...
> > Using the notation [A B C] for <NOT> (A <AND> B <AND> C), etc.
> >
> > The following [ A [B]] means "A implies B" for Boolean algebra.
What
> > is
> > the corresponding thing for Relational Algebra?
> >
> > Also, I'm trying to come up with a bracket notation for a "literal
> > relation", like literals for simple datatypes like numbers and
character
> > strings.
> >
> > I'm toying with this:
> >
> > [["David" "Cressey" 1]
> > ["Marshall" "Spight" 2]
> > ["Jan" Hidders" 4]]
> >
> >
> How about something like this
> {(Last, First, Num) :
> ("David", "Cressey", 1),
> ("Marshall", "Spight", 2),
> ("Jan", "Hidders", 4)}
>
> > This would represent a relation of order 3 and cardinality 4.
> >
> >
values
> > and attribute names is
> > by position rather than by name, and in fact the attribute names don't
> > even
> > appear here. That's unacceptably bad. The symmetry is appealing, but
it
> > clearly needs improvement.
> >
> >
> >
> > Does tutorial D have a way of laying out a relation as an explicit
literal
> > character string?
> >
> >
> >
> >
> >
>
>

I like the colon. I'd like to stay within the square bracket notation, if possible. Received on Tue Jul 17 2007 - 09:16:12 CEST

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