  The physical resources available to access and manipulate the degrees of
freedom of a quantum system define the set $\cal A$ of operationally relevant
observables. The algebraic structure of $\cal A$ selects a preferred tensor
product structure i.e., a partition into subsystems. The notion of compoundness
for quantum system is accordingly relativized. Universal control over virtual
subsystems can be achieved by using quantum noncommutative holonomies
