I'm trying to see the semantic difference between schema:affiliation and schema:memberOf. Is the former a sub-property of the latter - although not formally defined as such at the moment?
Yes, affiliation looks like a specialized case of memberOf to me. The latter also allows Orgs to be members of thing, and accepts programme membership as a kind of value. But I can't think of any case where x has an affiliation y, where we wouldn't also say that x is a memberOf y.
Made affiliation subproperty of memberOf - issue #596
documented #596 - affiliation subPropertyOf memberOf
Queued for publication, see http://sdo-ganymede.appspot.com/affiliation - thanks again