Re: Relational lattice
Date: Thu, 10 Mar 2005 21:13:15 GMT
Message-ID: <LL2Yd.34677$f73.3168353_at_phobos.telenet-ops.be>
Vadim Tropashko wrote:
>
> Is it possible to express transitive closure in a finite set of
> equations as well?
> BTW, I just came across
> http://c2.com/cgi/wiki?RelationalAlgebra
> describing the "simplified algebra in the Third Manifesto". (I confess
> that I don't have a copy of any manifesto book:-).
I won't tell. :-)
> The AND operator is
> a natural join, but the OR is defined differently! It is immediate,
> that the Third Manifesto definition doesn't respect the absorption law:
> A OR (A AND B) header should be the union of the A and B headers,
> therefore the result can't be A. Without absorption law the structure
> is merely a semilattice, where the order induced by the meet operation
> -- OR -- is different from the order induced by the join. The nice
> feature of the manifesto algebra is that it respects distributive law.
So, how about the cylindric set algebras? For a short description look for "Applications of Alfred Tarski's Ideas in Database Theory".
- Jan Hidders