The ICAO PANS-AIM requires in relation with the AIP data set that: “5.3.3.1.2 When a property is not defined for a particular occurrence of the subjects listed in 5.3.3.1.1, the AIP data sub-set shall include an explicit ‘not applicable’ indication.”
Using AIXM, it is possible to indicate a reason, such as ‘not applicable’, ‘unknown’, etc. for each property (attribute or association) that has no assigned value in the Data Set. This is done by assigning a suitable value to the nilReason attribute.
There exists a predefined list of values for this attribute, coming from the GML standard. In order to ensure that these values are unambiguously interpreted, their meaning and the use of this attribute are further detailed here.
Rule
The following values shall be used for the nilReason attribute:
- inapplicable - there is no value. It is normal that a value is not assigned because the corresponding real world artifact does not have this kind of property);
- unknown - the correct value is not known to, and not computable by, the sender of this data;
- withheld - the value is not divulged. A value exists, but it cannot be provided because it is subject to restricted use (for example, it is a military restricted data, it is commercially sensitive, etc.). Access to this data might be possible through direct contact with the data provider, in special circumstances.
Rule
When no value is assigned, a nilReason value shall be assigned to each attribute or association that is identified as ‘mandatory’ in the Data Set Coding Rules.
Note: This practically means that the data set does not comply with the rule specified in 3.2. However, this additional rule allows for the reason of non-compliance to be identified. The data set might still be usable for certain applications.
Rule
When no value is assigned, a nilReason value should be assigned to each attribute or association that is identified as ‘recommended’ in the Data Set Coding Rules.