A method for maintaining data objects in memory introduces metrics for freshness and interestingness of the data object. A freshness estimate is defined as the length of time that the data contained within the data object is expected to remain correct from the date that the object was last known to be valid. The interestingness estimate is defined as the length of time that the data object is expected to retain its usefulness to the user from the time that the data object was last used. The freshness estimate and interestingness estimate are stored in the data object along with a reference date. The freshness estimate, interestingness estimate, and reference date are updated or confirmed each time the data object is accessed. A maintenance program is periodically invoked to determine whether the data objects are outdated by comparing the time estimates associated with each data object to that object's reference date. Objects found to be outdated are candidates for removal from the system.