Changes only
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 airspace is active 07:00-21:00 MON-FRI and 09:00-13:00 SAT, SUN, LH. This information is encoded as a BASELINE where the status has the necessary associated Timesheets:
- AirspaceActivation with status='ACTIVE', MON-FRI 07:00-21:00, SAT, SUN, LH 09:00-13:00
- AirspaceActivation with status='INACTIVE', 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": status=INACTIVE, MON 19:00-21:00. However, that would be wrong because the airspace activation status would be undefined at any other time than MON 19:00-21:00. Remember that the TEMPDELTA replaces the BASELINE AirspaceActivation 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 AirspaceActivation with status='INACTIVE', MON 19:00-21:00
- a second AirspaceActivation (adapted from the BASELINE) with status='ACTIVE', MON 07:00-19:00, TUE-FRI 07:00-21:00, SAT, SUN, LH 09:00-13:00
- a third AirspaceActivation (copied from the BASELINE, for completeness sake) with status='INACTIVE', MON-FRI 00:00-07:00 21:00-24:00, SAT, SUN, LH 00:00-09:00, 13:00-24:00
It is strongly 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.