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• NUMBER
1the word 'entity' is used within this document in the entity-relationship sense; it is not an 'XML entity'
2http://www.eurocontrol.int/ais/ahead/eaip
4 Edition Number: 4.5
AIXM PRIMER
• ZNUMBER
• DEGREES1
• DEGREES2
were mapped directly to XML Schema types and restricted using facets. Other domains, such as:
• LATITUDE
• LONGITUDE
• DATE
• TIME
• DATETIME
were mapped as strings restricted by facet patterns. All of these types are used directly. Conversely,
domains such as ALPHA were declared as base types in the schema, and were then restricted by other
types. Mostly this construct was used for non-enumerated text types restricted by length, typically to
restrict names etc. to a particular selection of letters.
One important aspect of data types to contrast the above paragraph with the implementation of the
CHARACTER2 domain, which was mapped directly to the xsd:string type without restriction. It is used
for textual descriptions and remarks, and permits the use of any UNICODE character. In relation with
this, due attention should be paid to character encoding issues - see Appendix C.
2.5. Deprecated Elements
Certain AIXM feature types and properties (elements) have been deprecated in AIXM 4.0 and in AIXM
4.5. That means that, although the elements still exist in the XML Schema, their usage should be abandoned
as soon as possible. The reason they are still in the schema is "technical backwards compatibility":
i.e. to ensure that an AIXM message that is valid against a previous version is also valid against version
4.5.
Deprecated elements are marked in the AIXM XML Schema with <xsd:appinfo> annotation elements,
as shown below. These tags can be used to direct an implementing system to handle deprecated elements
as required.
<xsd:complexType name="DlnType">
<xsd:annotation>
<xsd:appinfo>DEPRECATED-4.0</xsd:appinfo>
<xsd:documentation>[Deprecated] DME - Limitation - Version</xsd:documentation>
</xsd:annotation>
...
</xsd:complexType>
An alternative, so-called "strict" version of AIXM 4.5, is also available, from which all deprecated elements
have been removed.
2.6. AICM Rules
In addition to information about entities, attributes and relationships, the AICM also contains textual
rules that cannot be represented using an entity-relationship model. These are classified into two types:
"technical" and "business", with business rules further classified into subcategories.
Edition Number: 4.5 5
AIXM PRIMER
A technical rule is one that is necessary in order to avoid data ambiguity, or, to put it another way, to
protect systems from data they cannot handle. A typical example are rules requiring a unit-of-measure
field to be present if a value field is present, such as shown below, taken from the DME definition in
the AICM:
"If VAL_DISPLACE is specified, then UOM_DISPLACE is mandatory."
Business rules are defined as "simple atomic statements that define or constrain some aspect of business
operations." They cannot be enforced in the AIXM XML Schema because there are often real-world
situations in which they can be broken, although the data may be correct. In addition, business rules are
often unenforceable using XML Schema. For example, the following rule, taken from the DESIGNATED_
POINT definition (on the CODE_ID attribute) is mandated by ICAO but cannot be captured
using XML Schema:
"If CODE_TYPE='ICAO', then CODE_ID should be unique world-wide."
It remains a task for every implementation of the model to decide to what degree such business rules
can be enforced.
The first of the two technical rules that have been implemented since version 3.3 of the AIXM, govern
the relationship between RWY (runway), RWY_DIRECTION (runway direction), and
RWY_CLINE_POINT (runway centreline point).
"The RWY_CLINE_POINT used as threshold must be related to the same RWY as the current
RWY_DIRECTION."
The XML schema originally contained the following construction for <Rdn> (runway direction):
<Rdn>
<RdnUid>...</RdnUid>
<RcpUid>...</RcpUid>
<valTrueBrg>...</valTrueBrg>
...
</Rdn>
Requiring the <Rdn> element to have an <RcpUid> (runway centerline point identifier) created an explicit
relationship to an existing runway centerline point . However, although both the <RdnUid> and
the <RcpUid> types contain a <RwyUid>, the schema could not prevent a dataset from using - wrongly
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