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- the runway centerline point of one runway as the threshold position for another runway. To eliminate
that possibility and to remove the duplicate <RwyUid>, the <RcpUid> element was replaced with just
<geo_lat> (latitude) and <geo_long> (longitude) elements. Therefore, when receiving an <Rdn> element
with explicit lat/long values, there must exist an <Rcp> for the same <Rwy> with exactly the same
lat/long values; if this is not the case, then there is an error somewhere.
A similar rule governs FATO (final approach and take-off area), FATO_CLINE_POINT (FATO centreline
point) and FATO_DIRECTION (FATO direction), and it has been encoded in a similar way.
"The FATO_CLINE_POINT used as threshold must be related to the same FATO as the current
FATO_DIRECTION."
6 Edition Number: 4.5
AIXM PRIMER
Chapter 3. Basic Concepts
3.1. AIXM Features Types
The basic AIXM information unit is the AIXM feature. A feature corresponds to a real thing in the
aeronautical environment, such as a navaid, runway, route segment, airport etc.. Each feature may have
attributes and relationships, all declared as child elements of the feature.
There are two levels in the definition of an AIXM feature. First, feature types are defined as complex
types in the AIXM-Features.xsd sub-schema file. Starting with AIXM version 4.5, these complex types
have un-abbreviated meaningful names, which are based on the content of the "full name" specified for
every AICM entity, followed by the keyword "Type". For example, the AD_HP_OBSTACLE entity
has "Obstacle at Aerodrome / Heliport" as full name. Therefore, the corresponding AIXM-Feature
complex type is named "AerodromeHeliportObstacleType".
In the second step, when used in AIXM messages, AIXM feature types are used to declare AIXM feature
elements. As explained in 2.3, short abbreviations of three letters are used for feature element names.
They start with an upper case character, while the remaining 2 characters are in lower case (for example,
'Vor').
For example, there exist a complex type "AerodromeHeliportType", having child elements such as
<txtName> - the name of the site, <codeIcao> - the ICAO Location Indicator, etc.:
<xsd:complexType name="AerodromeHeliportType">
<xsd:annotation>
<xsd:documentation>Aerodrome / Heliport</xsd:documentation>
</xsd:annotation>
<xsd:sequence>
<xsd:element name="AhpUid" type="AerodromeHeliportUidType">
…
</xsd:sequence>
</xsd:complexType>
3.2. Feature Attributes
Attributes from the entity-relationship model correspond to local child elements in the declaration of
the feature types. For example:
<xsd:element name="valFreq" type="valFreq">
<xsd:annotation>
<xsd:documentation>Frequency</xsd:documentation>
</xsd:annotation>
</xsd:element>
<valFreq> is a local child element in the definition of the complex type VorType, having as type 'valFreq'.
The latter is a simple type and corresponds to an entity-relationship attribute domain. All such simple
types are defined in the AIXM-Update-DataTypes.xsd sub-schema and the AIXM-Snapshot-Data-
Types.xsd sub-schema.
In general, all attributes from the entity-relationship model have an equivalent feature attribute in AIXM.
However, as the order of elements is significant in XML, many NO_SEQ attributes from the entity-relationship
model have not been included into the AIXM-Features sub-schema. For example, the NO_SEQ
attribute of the AIRSPACE_VERTEX entity does not exist in the definition of the Avx AirspaceBorderVertexType
in the XML Schema. This is also related to the fact that using AIXM it is only possible
to exchange data about an entire airspace border, not about individual border points (vertexes). If a
Edition Number: 4.5 7
AIXM PRIMER
border point has changed, then the whole border data, including all its points, must be included in AIXMUpdate
messages. This is due to the difficulty to identify individual vertexes in order to update them
separately. Adding a sequence number to every vertex was not considered necessary, because the order
of the child elements in XML already gives an implicit sequence. In addition, sequence numbers are
difficult to maintain when a vertex is added or deleted in the middle of the border definition. It was
consider safer to require the whole updated border definition to be included in the AIXM-Update message.
Feature attribute names have been derived from the corresponding attribute name in the entity-relationship
　
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