1. A method comprising: accessing a corpus stored in one or more tangible media, the corpus comprising a plurality of terms; performing the following for each term of one or more terms of the plurality of terms to yield a plurality of parent-child relationships: identifying one or more parent terms of the each term according to directional affinity, the plurality of terms comprising the one or more parent terms, the directional affinity being the number of co-occurrence contexts that include two terms, over the number of co-occurrence contexts that include one term; and establishing one or more parent-child relationships from the one or more parent terms and the each term; and automatically generating a hierarchical graph from the plurality of parent-child relationships, wherein the automatically generating the hierarchical graph from the plurality of parent-child relationships comprises reducing the hierarchical graph by: identifying a parent-child relationship and a redundant parent-child relationship of the hierarchical graph; and removing the redundant parent-child relationship from the hierarchical graph.