Re: A simple notation, again

"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]
> ["Bob" "Badour" 3]
> ["Jan" Hidders" 4]]
>
>
How about something like this
{(Last, First, Num) :

("David",  "Cressey", 1),
("Marshall", "Spight", 2),
("Bob", "Badour", 3),
("Jan", "Hidders", 4)}

> This would represent a relation of order 3 and cardinality 4.
>
>
> What I don't like about this is that the binding between attribute 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?
>
>
>
>
>
Received on Mon Jul 16 2007 - 20:05:34 CEST