def create_identity(attributes, start=nil)
      start ||= START_OF_TIME
      create(attributes.merge(START_COLUMN=>start || START_OF_TIME))
    end
def create_identity(attributes, start=nil)
      start ||= START_OF_TIME
      create(attributes.merge(START_COLUMN=>start || START_OF_TIME))
    end
The first iteration can be defined with a specific start date, but
 that is in general a bad idea, since it complicates obtaining
 the first iteration