A concept identifier is used in cases where several records can pertain to the same concept, in which instance the record identifiers for the various records will differ, necessitating the inclusion of a linking identifier in order to maintain the integrity of the overall concept entry. Concept identifiers are also essential in systematically organized terminologies, where they are used as cross-reference identifiers from alphabetical lists. They are also listed separately in environments where a stable entry identifier is needed, but the virtual entry identifier can be subject to change as a result of database management considerations.