Abstract: A computer system, methods, and programs for creating an index for aggregating data in at least one tree structure including at least one node each including one label indicating node type and values. The system includes a node ID assignment processing unit for assigning IDs to the nodes in a post order; first, second, and third index creation processing units. The first unit creates a first index having one or more sets of data including the node ID and values included in the node; the second unit creates a second index having one or more sets of data including node ID and ID of a descendant node having the minimum ID; and the third unit creates a third index having one or more sets of data including IDs of one or more nodes having specific values.

Abstract: Based on a probability of summary metadata associated with an entity of a media hosting service being inaccurate, a determination is made as to whether to verify the accuracy of the summary metadata. In response to determining to verify the accuracy of the summary metadata, a determination is made as to whether the summary metadata is inaccurate with respect to master metadata associated with the entity of the media hosting service. The summary metadata is updated with a correct value determined from the master metadata, in response to determining the summary metadata is inaccurate.