A more advanced way of doing this will be with something like this model, and archetypes based on it. We need to add a meta-type of the archetype model that allows a constraint for a thing like LINK (or CITATION in the above-mentioned model) to have the RM type of its target constrained, i.e. to say ‘this thing must point to an instance of type X at runtime’.
We don’t have this today, but in the next 6 months, I’d like to see it in the specs.