This representation makes it fairly easy to add attributes as needed. The vector Rt capturesthestateofalltheinventoriesbeingmanaged.Inaddition,amodelingframework isneededwhereparameterssuchasfailureratesareuncertainandarechangingovertime asnew information arrives. Allother forms of “knowledge”are represented using k t, and all information is captured using the state variable St, which means that the state of the system (the state of everything known about the system) is given by: