Note: some thoughts regarding virtual data and xbooks
Each activity in a xbook is a transformation. We can store a transformation id in an activity's properties folder and then register all application instances as derivations in the VDC. When a user requests an activity, we can first check to see if there is already a derivation existing in the VDC and fetch the data if it is. If a archived activity is re-executed with exactly the same parameters, then we can also grab the data from Chimera. If an archived activity is executed with one or more different parameters, then we can register it as a transformation.