1. A method for building a taxonomy, the method comprising: receiving, by a computer, one or more ancestor recommendations; generating, by the computer, an initial tree from a graph by pruning one or more paths of the graph; modifying, by the computer, the initial tree according to an evaluation of the initial tree in view of the one or more ancestor recommendations to generate an output tree by applying the one or more ancestor recommendations to each node of at least a portion of nodes of the initial tree having multiple immediate parent nodes in the graph effective to select a single selected immediate parent node for the each node and prune paths to immediate parent nodes of the each node other than the selected immediate parent node, the one or more ancestor recommendations applied effective to obtain a path from the selected immediate parent node within the initial tree to an ancestor node specified in the one or more ancestor recommendations; and outputting, by the computer, responses to queries in accordance with the output tree.