An important principle to be applied for the digital encoding of the event data is that only the changed data elements shall be provided. There is no need to include in a TEMPDELTA TimeSlice the data that is part of the BASELINE and which does not change. For example, if a Navaid is temporarily unserviceable, only the operational status of the Navaid shall be part of the AIXM encoding.
However, this general principle needs to be adjusted with the rules stated in the AIXM Temporality Concept - a "delta" can be encoded only for a first level feature property. A TEMPDELTA completely replaces the information contained in the BASELINE about the same property.
The following example indicates how the temporality rules apply in the case of a Tempdelta that modifies a property with an associated schedule:
Baseline situation: an airport is open 07:00-21:00 MON-FRI and 09:00-13:00 SAT, SUN, LH. This information is encoded as a BASELINE where the operationalStatus has the necessary associated Timesheets:
- AirportHeliportAvailability operationalStatus=NORMAL, MON-FRI 07:00-21:00, SAT, SUN, LH 09:00-13:00
- AirportHeliportAvailability operationalStatus=CLOSED, MON-FRI 00:00-07:00 21:00-24:00, SAT, SUN, LH 00:00-09:00, 13:00-24:00
Temporary (event): in Feb 2018 the airport is closed by NOTAM every MON 19:00-21:00 due to work in progress.
- the first temptation would be to encode it as a TEMPDELTA valid from MON 05 FEB 2018 at 19:00 - MON 26 FEB 2011 at 21:00 with just one Timesheet": operationalStatus=CLOSED, MON 19:00-21:00. However, that would be wrong because the airport operational status would be undefined at any other time than MON 19:00-21:00. Remember that the TEMPDELTA replaces the BASELINE AirportHeliportAvailability in full.
- a correct encoding needs to cover the full period of validity of the Tempdelta, including information from the BASELINE that is still applicable. This includes:
- one AirportHeliportAvailability with operationalStatus=CLOSED, MON 19:00-21:00
- a second AirportHeliportAvailability (adapted from the BASELINE) operationalStatus=NORMAL, MON 07:00-19:00, TUE-FRI 07:00-21:00, SAT, SUN, LH 09:00-13:00
- a third AirportHeliportAvailability (copied from the BASELINE, for completeness sake) operationalStatus=CLOSED, MON-FRI 00:00-07:00 21:00-24:00, SAT, SUN, LH 00:00-09:00, 13:00-24:00
It is recommended that the input interface provides a "calendar/level" view in such situations, enabling the operator to graphically check the status of the feature at different times and levels, as explained in the HMI recommendations for coding schedules.