WebHubTel, I agree that relational ologs provide a formalism for imposing logical constraints on a collection of triples, but I'd hesitate to say that it's "just adding Prolog to triples". For one thing, Prolog is usually interpreted in a special, fixed model (the minimum Herbrand model). But we even if we drop that restriction and interpret a Prolog program more liberally, like a typical first-order theory, it's not clear how regular logic and Prolog compare. On the face of it they look different, but I don't know Prolog very well, so maybe I'm wrong. It might be interesting to investigate further.