1. A method performed by at least one computing device, the method comprising: receiving a first terminology comprising first concepts and corresponding first codes; receiving a second terminology comprising second concepts and corresponding second codes; mapping the first concepts and the second concepts to levels of a combined hierarchical ontology; associating some of the first concepts and the second concepts within the combined hierarchical ontology; and providing programmatic access to the combined hierarchical ontology, wherein the providing programmatic access comprises: receiving a request identifying an individual first concept-code pair, the request identifying a number of levels to traverse the combined hierarchical ontology, the number of levels being greater than one; traversing the combined hierarchical ontology the identified number of levels to identify an ancestor concept-code pair of the individual first concept-code pair, and identifying, in the combined hierarchical ontology, a sibling concept-code pair of the individual first concept-code pair that shares the ancestor concept-code pair with the individual first concept-code pair but has a different meaning than the individual first concept-code pair.