The present disclosure includes systems and techniques relating to building and using hierarchical knowledge structures. In general, embodiments of the invention feature a computer program product and a method including receiving a first ontology including initial categories, an indication of sample data for a given category of the initial categories, and an indication of symbolic knowledge for the given category; and populating the first ontology with new features to form a second ontology, the populating comprising determining the new features from the sample data using a statistical machine learning process and retaining the new features and the symbolic knowledge within the second ontology in association with the given category. In another aspect, embodiments of the invention feature a knowledge management system including a hierarchical knowledge structure that categorizes information according to cognitive and semantic qualities within a knowledge domain.