1. A method of tuning a decision network comprising: identifying a deviation between a correct interpretation of a data item and an incorrect interpretation of said data item; in a decision network comprising a hierarchical set of nodes and leaves, determining a path of traversed nodes in said decision network resulting in said deviation, wherein said nodes correspond to queries; calculating a measure of goodness at a node in said path using at least one new query as a replacement for an existing query to determine whether said measure of goodness improves using said at least one new query compared to said old query; and if said measure of goodness improves, selecting said at least one new query and regrowing said decision network from said node down through said leaves using said at least one new query at said node.