A data structure for storing items of information having a time of life includes a time of life interval for each item of information, and methods for using the same. The items of information are organized in a data structure having nodes and edges connecting the nodes. This data structure is preferably a directed acyclic graph structure. The data structure includes parent nodes and child nodes. The time of life interval specified for any child node generally is contained within the time interval specified for that child node's parent node, such that the data structure includes no child nodes with a time of life interval that falls outside of the time of life interval of its parent node.