I would expect that how you solve this at least partially depends on how that data will be used.  If it is e.g. to be used for cross charging for the resource across departments, then is the resource allowed to belong to only one department or can it be more than one.  If only one, then maybe the person or HR is the one to pick what it is.  If many then maybe it is not really data to store, but data to be derived from time-sheets?