  It is argued that the partition of a quantum system into subsystems is
dictated by the set of operationally accessible interactions and measurements.
The emergence of a multi-partite tensor product structure of the state-space
and the associated notion of quantum entanglement are then relative and
observable-induced. We develop a general algebraic framework aimed to formalize
this concept. We discuss several cases relevant to quantum information
processing and decoherence control.
