16. A system comprising: one or more hardware processors; and one or more computer-readable storage devices storing computer-readable instructions which, when executed by the one or more hardware processors, cause the one or more hardware processors to: receive a sibling request to access a combined hierarchical ontology, the combined hierarchical ontology comprising first concepts and first codes associated with the first concepts by a first terminology and second concepts and second codes associated with the second concepts by a second terminology, wherein the sibling request identifies a specified first concept that is on a particular level of the combined hierarchical ontology and the sibling request specifies a number of levels to traverse the combined hierarchical ontology, the number of levels being greater than one; traverse the combined hierarchical ontology the number of levels specified by the sibling request to identify a common ancestor shared by the specified first concept and a corresponding second concept, wherein the corresponding second concept has a different meaning than the specified first concept and is also on the particular level of the combined hierarchical ontology with the specified first concept; and provide a response to the sibling request that identifies the corresponding second concept that shares the common ancestor with the specified first concept.
20. The system of claim 16 , wherein the response includes the corresponding second concept and does not include a corresponding second code of the second concept.