1. A method for use in a computer system, the method comprising acts of: storing a first content unit on at least one object addressable storage (OAS) system; storing a second content unit on the at least one OAS system; using the at least one OAS system to: identify the first content unit with a first object identifier that, from the perspective of an entity accessing the first content unit on the at least one OAS system, is independent of a first storage location of the first content unit on the at least one OAS system; and identify the second content unit with a second object identifier that, from the perspective of an entity accessing the second content unit on the at least one OAS system, is independent of a second storage location of the second content unit on the at least one OAS system; deriving content of the first content unit at least partially from content of the second content unit; and storing on the at least one OAS system a third content unit that comprises: the object identifier for the first content unit and metadata relating to the first content unit; and the metadata identifying the second content unit as a source from which the content of the first content unit is at least partially derived.