This won't make sense to most people, but I'm just taking notes for myself so I don't forget...
I notice in the Wikipedia entry on Category Theory the following:
"Relations among morphisms (such as fg = h) are often depicted using commutative diagrams, with "points" (corners) representing objects and "arrows" representing morphisms. The influence of commutative diagrams has been such that "arrow" and morphism are now synonymous."
This reminds me of the (recently neglected) idea of compositional statements in OWL. I require some formalism to make composition a viable suggestion, and this may be a starting point.
The problem with this approach is that predicates can't really be considered to be morphisms, as it is possible to repeat them many times on a given subject. (Does this mean that the predicates can't be morhpisms, or just that they can't be monomorphisms?) Still, I wonder how many category theory ideas are portable into RDF? In a moment of meta-meta insanity, I'm left wondering if there is a morphism from category theory to RDF?