1. Temporality and Encodings
Concepts and Examples
The purpose of this briefing is to familiarize you with the key concepts of AIXM and show an example encoding in XML.
Presented by Brett Brunk
Aeronautical Information Management (AIM) group
Federal Aviation Administration – United States
Singapore Workshop – Technical Focus - 16 June 2008

2. Topics Temporality Example AIXM 5 Encodings Why is it necessary
AIXM 5 temporality concepts
A NAVAID example
Example AIXM 5 Encodings
Components of an AIXM 5 exchange file
New Airspace
Temporary change to airspace usage
Today we’ll cover temporality. We will discuss why temporality is important, go over key temporality concepts and show an example.
Secondly we’ll look at the components of an AIXM 5 exchange file by reviewing an encoding new a new airspace. I’ll end the briefing by showing an example of a COTS tool that can load and discuss AIXM 5 temporal information.
Singapore Workshop – Technical Focus - 16 June 2008

3. Why do we need temporality?
Time is essential for aeronautical information
For operational reasons, distinction between:
Permanent changes
Temporary status
Two levels:
Life of the feature
Changes in properties
Why do we need temporality? We need it because time is an essential component of aeronautical information. Consider your own situation at your AIS office. How many times have you had to update your AIP because of a change? Have you issued a NOTAM making a temporary change? In both cases, you used temporality because you issued a change (permanent or temporary) that become effective over a specific period of time.
Temporality exists at two levels. One level we call the lifetime of the feature. In other words a feature like crane is created as an obstacle at one moment in time and later it can be dismantled and deleted. This is feature lifetime because it sets the time when the feature first begins and when it ends.
We also have temporality at the feature property level. While the crane exists, it can move or change height. We call these changes feature property timeslices because over a slice in time, the feature properties are constant. Between slices of time, the properties can change.
Singapore Workshop – Technical Focus - 16 June 2008

4. Temporality Model Definition Key assertions AIXM Temporality Model
A model that incorporates the concept of time
Key assertions
All features are temporal with start of life and end of life
Example, A new air traffic control sector
All features change over time
Example, A VOR is out of service for a day
AIXM Temporality Model
Relates features to the time extent in which they are valid
Provides various means to describe the time extent
A temporal model is one that incorporate the concept of time. In AIXM we recognize that all aeronautical data is temporal. Aeronautical features have a start of life and end of life. In addition aeronautical features can change over time. The AIXM temporality model is used to describe when features are valid and when feature properties change over time.
Singapore Workshop – Technical Focus - 16 June 2008

5. Time varying properties
Consider this feature (say it is a NAVAID) with properties P1 through P5. We can see that at any one moment in time the properties may have a value. For example P1 has value 1 at one time and later value 2. In addition, the value of a property may be null. By null, I mean the property is not specified. You can see that while a feature may exists, the value of its properties can change.
Singapore Workshop – Technical Focus - 16 June 2008

6. The basic Time Slice model
We can mark the times where the properties change with vertical lines. We can see that at one time P1 changed from value 1 to value 2. We can call this line an event – it is an event that led to the change of property P1. Events occur at instants of time when one or more properties change.
Singapore Workshop – Technical Focus - 16 June 2008

7. The basic Time Slice model
The intervals between events are called timeslices. Within a timeslice the properties of a feature are constant.
Singapore Workshop – Technical Focus - 16 June 2008

8. The basic Time Slice model
The constant set of properties within a timeslice describe the “STATE” of a feature. The STATE of a feature is defined as the value of a feature properties over a timeslice.
Singapore Workshop – Technical Focus - 16 June 2008

9. The basic Time Slice model UML
In AIXM 5 we model the basic temporality model using GML timeslices as shown. Here you can see the general AIXMFeature with its “identifier” property. The “identifier” property is the only property of a feature that doesn’t change in time. Each AIXMFeature exists over multiple timeslices. Each timeslice has a set of properties associated with it. Each timeslice has a “validTime” property indicating when the timeslice is effective. Each timeslice has a featureLifeTime property indicating the start and end of life for the feature.
Singapore Workshop – Technical Focus - 16 June 2008

10. Temporary events (digital NOTAM)
With AIXM 5 we also recognized the need for temporary events. These temporary events override one or more feature properties during a time interval. The temporary value is said to “overwrite” the permanent feature properties. When the temporary timeslice ends the property revents to the permanent timeslice value.
Singapore Workshop – Technical Focus - 16 June 2008

11. Temporary events Two kinds of Time Slices
Baseline = describes the feature state (the set of all feature’s properties) as result of a permanent change;
Temporary Delta = describes the transitory overlay of a feature state during a temporary event.
So to this point we have identified two types of timeslices.
The baseline timeslice describes the feature state as a result of a permanent change.
The temporary delta describes the transitory overlay of a feature state during a temporary event.
Consequently we add another property to our timeslice model called “interpretation” Interpretation tells us the type of timeslice we are describing.
Singapore Workshop – Technical Focus - 16 June 2008

12. Current status of a feature
We can expand the temporality model and include some additional timeslices that can be useful. We can identify a “snapshot” as the state of the feature at a time instant. It is the result of combining the baseline timeslice with any temporary timeslices in effect at the “snapshot” time.
SNAPSHOT = describes the state of a feature at a time instant, as result of combining the actual BASELINE Time Slice valid at that time instant with all TEMPDELTA Time Slices applicable at that time instant.
Singapore Workshop – Technical Focus - 16 June 2008

13. Permanent changes
We can identify a “PermDelta” timeslice at the permanent events. It is a type of timeslice that describes the difference in feature state between two permanent changes (baselines).
PERMDELTA = A kind of Time Slice that describes the difference in a feature state as result of a permanent change.
Singapore Workshop – Technical Focus - 16 June 2008

14. Time Slice Types
Together we can show all the types of timeslices on a single graphic.
Singapore Workshop – Technical Focus - 16 June 2008

15. Summary - Time Slice types
BASELINE = A kind of Time Slice that describes the feature state (the set of all the feature’s properties) as result of a permanent change;
PERMDELTA = A kind of Time Slice that describes the difference in a feature state as result of a permanent change;
TEMPDELTA = A kind of Time Slice that describes the transitory changes of a feature state during a temporary event;
SNAPSHOT = A kind of Time Slice that describes the state of a feature at a time instant, as result of combining the actual BASELINE Time Slice valid at that time instant with all TEMPDELTA Time Slices applicable at that time instant.
This slide summarizes the 4 types of timeslices in the AIXM 5 temporality model.
Singapore Workshop – Technical Focus - 16 June 2008

16. An Example: Navaid frequency change
Imagine that AML Navaid undergoes an upgrade that changes its frequency from 112 MHz to MHz…
Schedule permanent change to coincide with AIRAC update cycle
Shutdown AML before the upgrade
Perform the upgrade
Start AML in test mode to evaluate change
This slide illustrates the temporal model for a hypothetical NAVAID called AML. Imagine that the NAVAID is undergoing scheduled maintenance that will result in a new Frequency.
Before the frequency change the AIP publishes a baseline of the AML NAVAID indicating all of its properties. Before maintenance begins the AML NAVAID is taken offline for upgrades. This operational status change results in TemporalDelta1. Once the frequency change is made there is a permanent delta indicating a frequency change. A new Baseline starts at the new AIRAC cycle. Finally after the frequency change the NAVAID is placed in operational status = test. A second temporary delta is created for this operational status change.
In all this scenario generates 4 versions of the NAVAID. A version is created at the start and end of each delta.
Singapore Workshop – Technical Focus - 16 June 2008

17. An Example: Navaid frequency change
AML Navaid undergoes an upgrade that changes its frequency from MHz to MHz…
This slide illustrates the temporal model for a hypothetical NAVAID called AML. Imagine that the NAVAID is undergoing scheduled maintenance that will result in a new Frequency.
Before the frequency change the AIP publishes a baseline of the AML NAVAID indicating all of its properties. Before maintenance begins the AML NAVAID is taken offline for upgrades. This operational status change results in TemporalDelta1. Once the frequency change is made there is a permanent delta indicating a frequency change. A new Baseline starts at the new AIRAC cycle. Finally after the frequency change the NAVAID is placed in operational status = test. A second temporary delta is created for this operational status change.
In all this scenario generates 4 versions of the NAVAID. A version is created at the start and end of each delta.
Singapore Workshop – Technical Focus - 16 June 2008

18. Topics Temporality Example AIXM 5 Encodings Why is it necessary
AIXM 5 temporality concepts
A NAVAID example
Example AIXM 5 Encodings
Components of an AIXM 5 exchange file
New Airspace
Temporary change to airspace usage
Now let’s look at a sample AIXM 5 encoding.
Singapore Workshop – Technical Focus - 16 June 2008

19. AIXM is based on International Standards
Aeronautical Information Exchange Model (AIXM)
ISO Spatial
Extensible Markup Language (XML)
ISO Temporal
ISO Geography Markup Language (GML)
ISO Metadata
Universal Markup Language (UML)
Before I do that I want to talk about the components of the AIXM 5 model so you can better understand how we construct the AIXM 5 exchange / encoding format.
This slide shows that the AIXM Conceptual Model is built upon several ISO standards – spatial, temporal and metadata. We document the conceptual model in UML.
The Exchange standard is derived from the Conceptual Model and output as an XML Schema compliant with GML. GML is the Geographic Markup Language an ISO standard for representing geographic information in XML.
Conceptual standards
Exchange standards
Singapore Workshop – Technical Focus - 16 June 2008

20. Extensible Markup Language (XML)
Web Page HTML
<h2><a href="sdat2/html/download.htm"> SDAT 5.7 Release</a></h2>
<h3 class="byline">New Features >></h3>
<p> <ul>
<li>Create traffic collections based on a sector number. (Flights flown through specified sector(s))</li> …
XML – Extensible Markup Language
Have you looked at what is underneath a web page?
XML has a similar look to HTML
Computer readable
Electronic exchange
Vendor supported
XML Document
<RunwayDirection>
<Designator>20L</Designator>
<VFRPattern>RIGHT</VFRPattern>
</RunwayDirection> …
As you probably know, AIXM is an XML language for aeronautical data. But what is XML? XML stands for Extensible Markup Language. Have you ever looked at what is underneath a web page? You can do this in Microsoft Internet explorer by going to a web page, right clicking and selecting View Source. If you look under a web page you’ll see all these tags like <h2> and <li> that are used to tell the computer how to display the text and graphics.
Well HTML is a type of XML. HTML is a version of XML used for formatting information for display in a web browser. XML is a more generic term that describes any grammar using specific encoding rules.
HTML = Hyper Text Markup Language
XML = Extensible Markup Language
Singapore Workshop – Technical Focus - 16 June 2008

21. Key Concept: Geometry and GML
Geometry important property of aeronautical information
Airspace polygons
Airport Reference Points
Navaid location
One of the key components of AIXM is geometry. Most features have a location and even a shape. Examples are airspace polygons, airport reference points and NAVAID locations.
Singapore Workshop – Technical Focus - 16 June 2008

22. Key Concept: Geometry and GML
ISO Geography Markup Language (GML)
Vendor independent standard
Based on XML
Good industry adoption
AIXM is based on Geography Markup Language (ISO 19136). This is a vendor independent XML standard for representing geometries. An snippet is shown on this slide for a Polygon.
AIXM encodings are in GML XML format. Let’s look at an airspace.
Singapore Workshop – Technical Focus - 16 June 2008

23. Creating a new airspace
An AIXM Airspace Feature
<?xml version="1.0" encoding="UTF-8" ?>
<Airspace xmlns=“ xmlns:gml=" xmlns:xlink=" xmlns:xsi=" xmlns:gmd=" xmlns:gco=" xsi:schemaLocation=" ../xsd/AIXM_Features.xsd" gml:id="A00001">
<gml:identifier codeSpace="
0bf9537f-27f a75f e51</gml:identifier>
<timeSlice>
<AirspaceTimeSlice gml:id="VID001">…</AirspaceTimeSlice>
</timeSlice>
</Airspace>
Unique Identifier for the Airspace. Computer readable
Container for the timeslices that make up the airspace
Definition of the airspace
This example shows how an Airspace might be encoding in AIXM 5.
The first element is the <Airspace> element. The element includes the relevant schema references.
The <gml:identifier> is a GML property representing the universally unique identifier for the airspace. Universally unique means it is a worldwide key or name for the feature. In AIXM we encourge the use of Universally Unique Identifiers (UUID) as a standard for generating these keys.
Below ithe identifier is the <timeSlice> element where one or more feature timesclies are present. Each timeslice defines the feature state or change in feature properties depending on the type of timeslice.
Finally the </Airspace> feature ends.
Let’s look at the Airspace Definition in more detail.
End of the Airspace Feature
Singapore Workshop – Technical Focus - 16 June 2008

24. Creating a new airspace continued
<gml:identifier …>…</gml:identifier>
<timeSlice>
<AirspaceTimeSlice gml:id="VID001">
<gml:validTime>
<gml:TimePeriod gml:id="VID002">
<gml:beginPosition> T00:00:00</gml:beginPosition>
<gml:endPosition indeterminatePosition="unknown" /> </gml:TimePeriod>
</gml:validTime>
<interpretation>BASELINE</interpretation>
<featureLifetime>
<gml:TimePeriod gml:id="VID003">
<gml:endPosition indeterminatePosition="unknown" />
</gml:TimePeriod>
</featureLifetime>
… other properties
</AirspaceTimeSlice> </timeSlice>
</Airspace>
Period of validity for timeslice
Baseline timeslice containing all feature properties
Inside the <AirspaceTimeSlice> we have the time period of validity for the timeslice.
Following the validTime is the interpretation indicating that this is a BASELINE timeslice. Therefore this time slice indicates the permanent state of the feature over a time interval.
Finally the featureLifeTime indicates the overall start and end of life for the feature.
Below these mandatory fields are the other properties of the airspace. Let’s look at the specific airspace properties on the next slide.
Period of validity for the Airspace feature
Singapore Workshop – Technical Focus - 16 June 2008

25. Creating a new airspace continued
<gml:identifier …>…</gml:identifier>
<timeSlice>
<AirspaceTimeSlice gml:id="VID001"> …
<type>TSA</type>
<designator>EBT15</designator>
<name>LO-RENINGE UAV AREA</name>
<controlType>MIL</controlType>
<class>
<AirspaceLayerClass>
<class>G</class>
</AirspaceLayerClass>
</class>
<geometryComponent>…</geometryComponent>
</AirspaceTimeSlice>
</timeSlice>
</Airspace>
Airspace Feature properties
Here we see Airspace specific properties such as the designator. Below that is the <geometryComponent> where the airspace shape and volume are defined. Let’s look at the volume definition on the next slide.
Airspace shape and volume
Singapore Workshop – Technical Focus - 16 June 2008

26. Creating a new airspace continued
<gml:identifier …>…</gml:identifier>
<timeSlice>
<AirspaceTimeSlice gml:id="VID001"> …
<geometryComponent>
<AirspaceGeometryComponent>
<theAirspaceVolume>
<AirspaceVolume>
<upperLimit uom="FL">95</upperLimit>
<upperLimitReference>STD</upperLimitReference>
<lowerLimit uom="FT">4500</lowerLimit>
<lowerLimitReference>MSL</lowerLimitReference>
<horizontalProjection> … </horizontalProjection>
</AirspaceVolume>
</theAirspaceVolume>
</AirspaceGeometryComponent>
</geometryComponent>
</AirspaceTimeSlice>
</timeSlice>
</Airspace>
Upper and lower limits
Here we see the geometryComponent defined. First the upper and lower limits are set. Next the <horizontalProjectiion” is specified as a GML surface.
GML definition of horizontal boundary
Singapore Workshop – Technical Focus - 16 June 2008

27. Creating a new airspace continued
<gml:identifier …>…</gml:identifier>
<timeSlice>
<AirspaceTimeSlice gml:id="VID001"> …
<geometryComponent>
<AirspaceGeometryComponent>
<theAirspaceVolume>
<AirspaceVolume>
<horizontalProjection>
</horizontalProjection>
</AirspaceVolume>
</theAirspaceVolume>
</AirspaceGeometryComponent>
</geometryComponent>
</AirspaceTimeSlice>
</timeSlice>
</Airspace>
<horizontalProjection>
<Surface gml:id="VID005" srsName="urn:ogc:def:crs:OGC:1.3:CRS84">
<gml:polygonPatches>
<gml:PolygonPatch>
<gml:exterior>
<gml:LinearRing>
<gml:pos> </gml:pos>
<gml:pos> </gml:pos>
<gml:pos> </gml:pos>
<gml:pos> </gml:pos>
</gml:LinearRing>
</gml:exterior>
</gml:PolygonPatch>
</gml:polygonPatches>
</Surface>
</horizontalProjection>
The GML for defining the horizontal project is shown in the inset.
Singapore Workshop – Technical Focus - 16 June 2008

28. Demonstration Viewing AIXM features in a commercial product
LuciadMap’s prototype AIXM Viewer
As a final step let’s look at the airspace in a COTS tool -- Luciad’s prototype AIXM Viewer. This shows the power of AIXM 5 and standards. The Luciad viewer can read and display the airspace because it understands AIXM 5 standards including GML.
Singapore Workshop – Technical Focus - 16 June 2008