Re: Transitive Closure

"Alfredo Novoa" <alfredo_at_ncs.es> wrote in message news:e4330f45.0405180244.9d5d351_at_posting.google.com...
> mikharakiri_nospaum_at_yahoo.com (Mikito Harakiri) wrote in message
news:<8a529bb.0405171058.36a5a26_at_posting.google.com>...
>
> > So we are talking about different algebra, that has a universe with
> > elements being unary relational algebra operators only -- selection,
> > projection,
>
> They are binary operators. Restriction has two operands: a relation
> and a boolean function, and projection a relation and a set of
> attributes.

Boolean function on what space? In other words, how many arguments this function has? Hint: how do you accomodate "weight < 10" predicate?

> > Cartesian Power (as product is, unfortunately, binary
> > operator)
>
> It could be defined as an n-ary operation like: join, semijoin, union,
> intersection, etc.
>
> *(a,b,c) = *(a,c,b) = *(b,a,c) = *(b,c,a) = *(c,a,b) = *(c,b,a)

What '*', and letters mean there?

> >, transitive closure, and, perhaps, negation. In this tiny 4
> > element universe we define one binary operation: composition of unary
> > relational operators.
>
> Which composition?

http://mathworld.wolfram.com/Composition.html http://en.wikipedia.org/wiki/Functional_composition Received on Tue May 18 2004 - 19:54:36 CEST