19. The system of claim 16 , wherein identifying differences comprises: retrieving the monitored document; and comparing the logical entities in the monitored document to the logical entities in the updatable reference.
19. The system of claim 16 , wherein identifying differences comprises: retrieving the monitored document; and comparing the logical entities in the monitored document to the logical entities in the updatable reference. 20. The system of claim 19 , wherein the identifying of one or more differences occurs at specified intervals.