Which might be more common, someone asking to which physical object does this virtual object relate?? or which virtual objects refer to this physical object?.

One more question, if a physical object has 10 virtual descendants which would be more common, a separation of 10 levels between the physical object and the leaf-level virtual object (i.e. each virtual object has only one descendant) or a separation of far less that 10, maybe 2 (e.g. physical object has one virtual child and that virtual object has 9 virtual object children).