> > If one has one dataset (say) and wants to find other datasets that
might be usefully combined with it to do some analysis, it would (I think) be useful to have something like this to help with the discovery. OK, but I'm not seeing is how this extra imaginary dataset helps with discovery, either. Isn't a type-assertion pretty much exactly what you're saying here: a statement that this entity belongs to a set (which may or may not be completely enumerated in any one place, or even at all)? So what is this implied dataset doing that the type assertions are not?
