1. A physical storage medium storing code representing instructions that when executed by a computer cause the computer to: produce a hierarchical ontology including a plurality of concepts; prohibit a link between a first concept from the plurality of concepts and a second concept from the plurality of concepts when a link between a parent concept linked hierarchically with the first concept and a parent concept linked hierarchically with the second concept is prohibited, the first concept being at any level within the hierarchy below a level of the parent concept associated with the first concept, the second concept being at any level within the hierarchy below a level of the parent concept associated with the second concept; and provide a user with access to the hierarchical ontology.