A system is configured to: (a) ingest a set of codes from a code reference, the code reference including words and non-words; (b) associate the set of codes to a set of representations, forming descriptive links between the set of codes and the set of representations; (c) ingest an unstructured document having a general outline, the unstructured document including (i) at least one of the words in the code reference, (ii) at least one code in the set of codes, or (iii) both (i) and (ii); (d) determine an ontology from content of the unstructured document with an unsupervised learning algorithm; and (e) store the determined ontology in a database, the ontology having an acyclic directed graph structure.