[SYMBOL] [A] [B] [C] [D] [E] [F] [G] [H] [I] [J] [K] [L] [M] [N] [O] [P] [Q] [R] [S] [T] [U] [V] [W] hierarchies      aggregation          revised procedure      CREATE TABLE statement      defined      general hierarchies          implementation      manipulating recursively      multilevel operations      permissions, creating      service information      specialized hierarchies      stepping through recursively      trees  2nd          nodes          root      vertexes         adding          deleting      vertices         most expensive