1. Digital AIM Training - AIXM
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2. AIXM UML modelling - essentials
Digital AIM Training - AIXM
AIXM UML modelling - essentials
AIXM uses the UML standard for defining its structure and content. This was defined by the OMG (Object Management Group) international organisation.
"The Unified Modelling Language (UML) is a graphical language for visualizing, specifying, constructing, and documenting the artifacts of a software-intensive system. The UML offers a standard way to write a system's blueprints, including conceptual things such as business processes and system functions as well as concrete things such as programming language statements, database schemas, and reusable software components.“
The following slides will explain some key constructs used in the AIXM UML model.
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3. AIXM UML modelling - essentials
Digital AIM Training - AIXM
AIXM UML modelling - essentials
UML is a widely used modelling methodology, developed primarily for “object oriented” software engineering. We are only using UML “class diagrams”, with the following main elements:
A UML class is the abstraction of a concept in the application domain. A class is shown in a class diagram as a rectangle giving its name e.g. Aircraft.
Properties represent structural features of a class. Properties are a single concept but they appear in two quite distinct notations: Attributes and Associations. Although they look quite different on a diagram, they are really the same thing.
Attributes are represented as a line of text in the second compartment of the class symbol. In the example, the Aircraft class has the following attributes:
stallSpeed
mass
type
You can now say that an Aircraft has a stallSpeed, has mass and has a type.
Each attribute may define its type (for example, CharacterString, Real or DateTime).
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4. AIXM UML modelling - essentials
Digital AIM Training - AIXM
AIXM UML modelling - essentials
Associations express the relationship between classes. UML represents an association between two classes by drawing a line between their symbols.
The role on the association end describes how the related class is used. In the example you can say:
The Aircraft has a property ‘manufacturer’. This is the role of AircraftManufacturer in the association.
You can also say that an AircraftManufacturer ‘manufactures’ Aircraft.
It is sometimes necessary to have unidirectional navigability. This is shown by adding an arrow at the destination end of the association. This means that the association is easily navigated in the direction indicated by the arrow. This does not mean that the associations cannot be navigated in the other direction but the directionality is a hint that implementations should make the navigation in the primary direction convenient and efficient. One class knows about the existence of the other in the direction of navigation but the reverse is not necessarily true.
The multiplicity of a property is an indication of how many values are allowed for that property. In AIXM, this is only used for associations. Multiplicity of [0..1] means that the attribute is optional i.e. it can appear once or not at all.
That’s pretty much all you need to know in order to have a high-level understanding of the AIXM UML Model. Another modelling artifact used in AIXM is inheritance, but that will be explained directly with an AIXM example in one of the next slides.
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5. Digital AIM Training - AIXM
AIXM scope
This slide gives an overview of the AIXM packages, which are used to identify high-level subject areas, such as airport, airspace, routes.
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6. Digital AIM Training - AIXM
AIXM Feature
This slide shows the attributes of the AIXM UML class that models an airport or a heliport. You can recognize well-known properties such as:
ICAO location designator
IATA 3 letter designator
Name
Field elevation
Transition level
Etc.
Note that other airport properties do not appear as direct attributes of the AirportHeliport class, but as associations with other classes. This will be shown in the next slides.
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7. AIXM feature vs. AIXM object
Digital AIM Training - AIXM
AIXM feature vs. AIXM object
This diagram shows that the AirportHeliport class uses an ElevatedPoint as aerodrome reference point (ARP). The main reason to encapsulate the properties of an elevated point in a separate class instead of including them directly in the AirportHeliport class is that other AIXM features, such as navaids, also need the same position attributes. Therefore, it is more economical for the model to declare the ElevatedPoint once, as a complex “object” class and then to re-use it through associations when needed.
Also note in this example the presence of the geoid undulation attribute in the ElevatedPoint class, which is an ICAO requirement – should be used to encode the value of the local difference between the WGS84 ellipsoid and the geoid.
This diagram also shows a feature (SurveyControlPoint) that is not typically present in the AIP. However, such survey control points are established on the airport surface in relation with WGS surveys, for example. The AIXM model goes beyond the pure AIP data, including information (such as survey points) that is necessary for applications such as digital airport maps.
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8. Digital AIM Training - AIXM
Associations
This diagram shows other associations of the AirportHeliport feature:
Served city - note the 0..* (zero to many) multiplicity, indicating that one airport can serve multiple cities
Note also how the different responsibility levels between an OrganisationAuthority and an AirportHeliport is modelled. This is more easier to read using the AIXM Wiki, where by clicking on the corresponding class in the diagram the details of each attribute are shown. This includes data types and enumerated lists of values:
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9. Digital AIM Training - AIXM
Data types
Some data types that are used in the navaid model:
Runway types (remember that in AIXM 4.5 these were two distinct entities
Civil/military status
Operational status – which is not needed for a static AIS database, but is typically used in NOTAM. This demonstrate the efforts made in order to enable AIXM 5.1 to provide digital NOTAM.
Note the presence of the nilReason attribute.
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10. Application – an example of input forms
Digital AIM Training - AIXM
Application – an example of input forms
What is the impact of this model on AIS?
The AIXM model is used by software development companies to develop applications that can store and process aeronautical information data. The typical example is a database for encoding AIP data. The correctness and completeness of the model is critical: if a property is not correctly modelled, it will not be available in the expected way to the data encoding operator. For example, if an error was made and the name of an airport was modelled as a number or with an insufficient number of characters, then it would be impossible to encode real airport names in that database. Even more important than this are missing attributes. For example, ICAO has recently introduced in Annex 15 requirements for providing airport certification information – authority and date of certification expiration. If this was not capture din the model, then the database data input forms will not include an data entry filed for this piece of data.
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11. Application – an example of input forms
Digital AIM Training - AIXM
Application – an example of input forms
You can see in this screen that the encapsulation of the Elevated point in a separate class in the AIXM UML model may also trigger it to appear on a separate form in the database interface. This is typically the case for multiple occurring properties, such as servedCity.
The screenshot at right shows another important aspect of AIXM 5.1 – the possibility to provide free text remarks and descriptions (called Notes) in multiple languages. This is particularly important for the adoption of AIXM world-wide.
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12. Digital AIM Training - AIXM
AIXM - Wiki
The AIXM Wiki provides a complete description of the AIXM UML model:
Probably the most useful function of the Wiki is “Search”.
What would you like to search for?
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13. Digital AIM Training - AIXM
Questions?
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