More details on that hereFrom a hierarchical point of view, everything can have more than one parent (comparable to cloning and/or tagging) -Another Example:-I am working on 50 drawing files whose Grandparent is USAThey have various parents depending on which State they are related to e.g. Maine, Virginia, etcI am preparing an invoice for work done on 20 of these filesso I copy these 20 files/item