1. A computer-readable storage device comprising instructions that, when executed by a computer, cause the computer to: receive a concept hierarchy, wherein the concept hierarchy identifies concepts associated with a document corpus, wherein newly created documents are without user intervention added to the document corpus and deleted documents are without user intervention removed from the document corpus based on information from one or more monitoring agents; generate an interface based on the concept hierarchy, wherein the interface is operable to navigate, search, and modify the concept hierarchy; transmit the interface for display to a display device; receive a search query; and in response to the search query: search the document corpus using the search query; and search the concept hierarchy for one or more concepts that are semantically related to the search query.