One embodiment of the invention provides method for processing a database query that includes an episode-based condition. The method includes determining the time periods associated with one or more duration episodes by analyzing a set of data reflecting values for the episode-based condition captured at various points in time. An episode definition may indicate the substantive data value associated with a duration based event, and the data values used to determine a beginning and ending date/time associated with each episode. Database queries that include the episode-based condition may be composed by specifying a desired value for the episode-based condition used in selecting query results.