A method to produce a history of at least a portion of a database comprising: providing a data store that includes a record indicating a first event associated with first data that describes a subject matter, and indicating a first time interval during which the first data is effective with respect to the subject matter and indicating a second time interval during which the first data is current with respect to the database; and adjusting the data store upon an occurrence of a new event to, update a first record indicating the first event associated with first data and indicating an end time of the first time interval, and add a second new record indicating a second event associated with second data that describes the subject matter, and indicating a start of a new first time interval that is substantially continuous with an end time of the first time interval and during which the second data is effective with respect to the subject matter and indicating a start of a new second time interval during which the second data is current with respect to the database.