The case that Dan describes is modeled quite often in IT: in any business system that deals with staff. It is standardly modeled as a Position, being an association between Person and Organization; and having a Role, duration, etc.
CERIF generalizes this greatly, by modeling associations between any two core entities in a generic way. They use this to describe e.g. departments (Org-Org), positions, temporary assignments (Person-Org), boss, supervisor, reporting lines, collaborators (Person-Person), project leaders, staff, reviewers (Person-Project), etc etc. IMHO the modeling of Position as a group (singleton at any given time) is neither straightforward nor completely adequate. E.g. how do you: - record that Obama acted in his capacity of US President? - connect the US to the position of US President?
