Abstract: Service items at a central authority are scheduled as to their selective availability upon user request at remote stations. These are bidirectionally connected to the central authority. Each service item is assigned to one or more structures of items. Each structure of items is assigned to one or more of a set of navigation contexts. One unique start instant in absolute time is assigned to each respective navigation context. Upon attaining of any such start instant, all service items assigned to the associated navigation context are rendered available unto a detected request.