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that are affected by the change. Even if present in the AIXM-Update message, the 'mid' attributes will
be ignored. However, the EAD system will fill-in the 'mid' attributes when issuing AIXM-Update or
AIXM-Snapshot messages. This might be useful for systems downloading data from the EAD.
5.1.4.4. Changed Natural Key
Changes that affect the natural key of the feature are encoded as in the example below. The <Changed>
element shall contain first the previous natural key of the feature instance (<VorUid> in this example)
and then new <Vor> element, including its new natural key and the rest of its attributes and relationships.
Again, as explained above, the 'mid' and the 'chg' attributes are optional.
…
<Changed>
<VorUid mid='187652432'> <!-- the old natural key -->
<codeId>BXL</codeId>
<geoLat>514333.34N</geoLat>
<geoLong>0032301.21E</geoLong>
</VorUid>
<Vor>
<VorUid mid='187652432'> <!-- the new natural key -->
<codeId>BXL</codeId>
<geoLat chg="1">514326.67N</geoLat>
<geoLong chg="1">0032345.37E</geoLong>
</VorUid>
<OrgUid>
<txtName>BELGIUM</txtName>
</OrgUid>
<txtName>BRUSSELS VOR</txtName>
<codeType>DVOR</codeType>
<valFreq chg="1">119.00</valFreq>
<uomFreq>MHZ</uomFreq>
<codeTypeNorth>MAG</codeTypeNorth>
<valDeclination>1.3</valDeclination>
<codeDatum>WGE</codeDatum>
<Vtt>
<codeWorkHr>H24</codeWorkHr>
</Vtt>
<txtRmk>This is just an example</txtRmk>
</Vor>
</Changed>
…
As mentioned before, the AIXM Schema was created starting from the AIXM entity-relationship model.
If applied as such in a relational database, the model would not allow for changes of the natural key to
occur. However, the AIXM Schema allows for changes of the natural keys. The AIXM entity-relationship
model should not be used as such (1:1) for a database implementation. Its main purpose was to facilitate
the generation of the AIXM Schema and it may contain modelling structures that are not appropriate
for a straight-forward relational database implementation. Implementers of the AIXM entity-relationship
model should perform a rationalisation of the model before implementing it in a physical database.
18 Edition Number: 4.5
AIXM PRIMER
5.1.5. Withdrawn Feature
A <Withdrawn> element contains data about one feature instance, which will no longer exist starting
from the effective date of the AIXM-Update message. The rule is that only the unique identifier of the
feature instance must be specified in a <Withdrawn> element.
For example, a type of fuel which is no longer available at the Brussels airport could be encoded as it
follows:
…
<Withdrawn>
<FulUid>
<AhpUid>
<codeId>EBBR</codeId>
</AhpUid>
<codeCat>AVGAS</codeCat>
</FulUid>
</Withdrawn>
…
5.1.6. Corrections to AIXM-Update messages
Data updates through AIXM-Update messages are normally issued long time in advance before their
effective date. For operationally significant changes, the AIRAC cycle shall apply. Particular implementations
might have even longer lead periods between the date when the changes are committed and their
effective date.
In this document the term pending data is used to designate data, which has already been published
(through an AIXM-Update message), but which has not reached yet the effective date.
There is an obvious need to be able to issue corrections to pending data. This is especially true for implementations
such as the EAD, which perform coherence checks involving pending changes of adjacent
States. AIXM-Update messages could be used as well in order to correct pending data. The convention
would be that when a feature version with the same effective date and the same natural key is issued by
a system, this new version overwrites the previously sent change.
There are some questions with how different combinations of the update primitives
New/Changed/Withdrawn should be interpreted. For example, a 'withdrawn' of a pending 'new' feature
should have as consequence that the feature will not be created at all. There are also combinations that
do not make sense, such as sending a 'new' after a 'changed'.
However, particular implementations may define their specific mechanism for corrections. In future
versions, it will be possible to include a correction mechanism in the AIXM Schema.
　
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