Data set variants

Introduction

The AIXM Temporality Concept based on "time slices" enabled indicating the time applicability (validity) of the information at the level of each feature instance. In addition, the validity of the data set as a whole can be specified using the data set metadata. As AIS data sets contain primarily information of lasting character, the time applicability is usually limited to providing the start of validity date and time, while the end of validity is typically undetermined. When updates of data sets need to be provided, the ICAO Annex 15, section 6.3 indicates that:

“6.3.3.1 Data sets shall be amended or reissued at such regular intervals as may be necessary to keep them up to date.

6.3.3.2 Permanent changes and temporary changes of long duration (three months or longer) made available as digital data shall be issued in the form of a complete data set or a sub-set that includes only the differences from the previously issued complete data set.

6.3.3.3 Recommendation.— When made available as a completely re-issued data set, the differences from the previously issued complete data set should be indicated.”

According to Annex 15, item 6.3.3.2, when changes occur, States have the option to either re-issue the complete data set or to publish an update that contains only the differences. Both options are supported by the AIXM Temporality Concept. The provision of just a list of differences puts the effort of compiling the resulting data set on the AIS clients. As update files will accumulate, this tasks risks to become increasingly complex and to alter the integrity of the data set. Therefore the regular provision of a complete/consolidated data set is considered a mandatory minimal service. This will provide both a ready-to-use data set and the possibility to verify the completeness of a client database that is maintained through data set updates.

Many traditional AIS clients, such as other State AIS, data houses and flight planning service providers, maintain their own aeronautical databases. Such users are primarily interested in receiving regular updates in order to keep their local data up to date. Therefore, the provision of the differences (new/changed/deleted) as compared to the previous data set issue is also recommended.

The Annex 15 requirement specified in paragraph 6.3.3.2 indicates that temporary changes of long duration (the equivalent of digital AIP SUP) should also be part of the digital AIS data sets. In most cases, this will require the use of 'TEMPDELTA' timeslices, similar to the coding of short duration and last minute updates (Digital NOTAM). Not all AIS clients might be interested or able to use this data. Therefore, providing such temporary updates in a separate data set instances is considered the best approach.

Based on the above considerations, the following variants of digital data sets are defined:

Baseline - contains all and only Baseline TimeSlices that are or become valid at the start of the time validity of the data set;
Difference - contains the difference between two consecutive Baseline DS as follows:
- mandatorily, all BASELINE TimeSlices that either end or start their validity at the start of the time validity of the data set. Optionally, equivalent PERMDELTA TimeSlices may be also provided, which have the advantage that they can indicate a bit more precisely the location of the change.
- if applicable, BASELINE TimeSlice that ended or started their validity at an intermediate time between the start of validity of two consecutive Baseline DS. This covers for data changes that may exceptionally occur outside the regular update cycle.
Supplementary - contains TimeSlices that correspond provide temporary updates with a validity of three months or longer (the equivalent of AIP SUP data), in the form of TEMPDELTA (for pre-existing AIXM features) or BASELINE (for new temporary AIXM features).

Baseline AIS Data Set

This data set variant is primarily intended for clients who are interested in a complete data set for the next cycle and that are not interested to directly see the differences from the previous period.

Rule

For each applicable effective date/time, a Baseline AIS Data Set shall be provided comprising for all features that are in the scope of the AIS data set:

The TimeSlices with interpretation BASELINE that fulfill the following criteria:

are valid or become valid at that effective date/time;
and have un undetermined end of validity.

Note: According to the AIXM Temporality Concept, the term "valid" TimeSlice designates either the single TimeSlice or the one with the highest correctionNumber between the TimeSlices with the same interpretation and with the same sequenceNumber.

The diagram to the right indicates the TimeSlices that shall be included in the complete AIS Data Set

Difference AIS Data Set

This data set variant is primarily intended for clients who are interested to directly see the differences in the data between two consecutive updates. Such clients are likely to have their own copy of the data, which they maintain by processing the differences. A complete Baseline data set variant could be used from time to time for consistency checks.

A 'difference' data set may be provided in two forms - with BASELINE TimeSlices or with PERMDELTA TimeSlices. These may be combined in a single file.

Using BASELINE TimeSlices

Rule

As a complement to each Baseline AIS Data Set, for each applicable effective date/time a Difference AIS Data Set (using BASELINE TimeSlices) shall be provided, comprising for all features that are in the scope of the AIS data set:

the TimeSlices with interpretation BASELINE that become active on the effective date/time;
the correction TimeSlices with interpretation BASELINE that have their period of validity ending on the effective date/time.

The diagram to the right indicates the TimeSlices that shall be included in the AIS Difference Data Sett, when coded with BASELINE TimeSlices.

Using PERMDELTA TimeSlices

Rule

As a complement to each Baseline AIS Data Set, for each applicable effective date/time a Difference AIS Data Set (using PERMDELTA TimeSlices) should be provided, comprising for all features that are in the scope of the AIS data set:

the TimeSlices with interpretation PERMDELTA that correspond to the BASELINE that become active on the effective date/time ;
the TimeSlices with interpretation PERMDELTA that correspond to the correction TimeSlices with interpretation BASELINE that have their period of validity ending on the effective date/time.

The diagram to the right indicates the TimeSlices that shall be included in the AIS Difference Data Set, when coded with PERMDELTA TimeSlices.

Supplementary AIS Data Set

This data set variant contains temporary changes of long duration, such as temporary obstacles, work areas at the aerodrome, etc. It is the digital equivalent of an AIP Supplement.

The Supplementary Data Set is not intended as an exception from the AIRAC cycle rules. Operationally significant changes shall be made at AIRAC dates and provided as digital data complying with the AIRAC cycle rules!

Recommendation

If applicable, for each applicable effective date/time a Supplementary AIS Data Set should be provided, comprising for all features that are in the scope of the AIS data set:

the TimeSlices with interpretation BASELINE, that:
- are valid on the effective date/time or that will become valid before the next intended update date/time of the data set;
- and that have a limited lifetime, which exceeds 90 days.
the TimeSlices with interpretation TEMPDELTA, if applicable, that:
- are valid on the effective date/time or that will become valid before the next intended update date/time of the data set;
- and that have a limited lifetime, which exceeds 90 days.

The diagram to the right indicates the TimeSlices that shall be included in the Supplementary AIS Data Set.