Patent ID: 7117491

Claim:
A computer implemented method for determining whether data has been modified, comprising: receiving one node associated with at least one data unit and a last version number; processing a data structure having a plurality of nodes, wherein there is one node associated with each data unit and at least one node that is capable of aggregating one or more nodes, wherein version numbers are associated with the nodes, wherein the data structure indicates a relationship of nodes, wherein one node is directly associated with each data unit, and wherein further aggregate nodes aggregate any one or more nodes in the data structure; determining from the data structure one node that is associated with the data units associated with the received node; determining that the at least one data unit associated with the received node has been modified if the received last version number is less than a version number of the determined node; determining an update to one data unit; setting the version number of the node directly associated with the data unit to an incremented highest version number for a node in the data structure; and for each aggregate node that aggregates the node directly associated with the data unit, setting the version number of the aggregate node to the incremented highest version number if the aggregate node does not aggregate one other node having a version number greater than the incremented highest version number.