A machine receives a description of the relationships among members of a data set. The machine constructs a graph that represents the relationships among the members of the data set, organizing the members of the data set into groups. The groups are analyzed to determine their relative strengths. Unbalanced groups can be balanced by splitting off heavy sub-trees that include too large a percentage of the nodes in the group. The machine can then use the graph to answer queries about members of the data set.