If the prices for a service change according to the date, this can be recorded in a view which contains a field for the name of the service, a field for the date and a field for the price. The field for the name of the service is the non-time-dependent part of the key and the field for the date is the time-dependent part of the key. If the view has maintenance status ‘M’, it is possible to insert records whose service name is identical to that of existing records. It is not possible, on the other hand, to insert records with new names into the view.