a management system monitors the storage system for changes in predefined attributes and issues event messages upon detection . a storage collector communicating with the management system responds to the event messages by selectively filtering those pertinent to the billing function . the storage collector generates usage event records that are then further processed by accessing the management system to ascertain if there are any related data objects associated with the object that gave rise to the attribute change . such additional information is then associated with the usage event and stored for later use by a billing application .