Is declarative programming going to become more important for the richer client web? I've been playing around with Ajax programming. It's easy, but one thing keeps coming up: the coupling of front and back-end. I see it as a possible source of duplication. It's not like it's a new problem either. I've seen several projects where the client and server validation code was duplicated. It's insane to write the same code in two or more languages! Why not just one?