1AIXM Users’ Conference, 18-20 March 2008

Implementing AIXM in Instrument Flight Procedures Automation

Presenter:Presenter:Iain HammondIain Hammond

MacDonald, Dettwiler & Associates LtdMacDonald, Dettwiler & Associates Ltd

AIXM Users’ ConferenceAIXM Users’ ConferenceMarch 18-20, 2008March 18-20, 2008Washington, DC Washington, DC

2AIXM Users’ Conference, 18-20 March 2008

Introduction

• Key Implementation Decisions

1. Used XSLT technology rather than data binding to reduce code base, and improve maintenance agility.

2. Used standard query & filter models to generalize the interface to AIXM features:

• Open Geospatial Consortium (OGC) Web Feature Service (WFS)• OpenGIS® Filter Encoding.

3. Extended AIXM model for FAA instrument flight procedure processes.

4. The use of Xlink associations - were the most challenging aspect of AIXM 5.0 to implement.

• The Instrument Procedure Development System (IPDS) and selected FAA databases were successfully integrated using web services and AIXM 5.0 RC3 in mid-Feb 2008.

3AIXM Users’ Conference, 18-20 March 2008

Instrument Procedure Development System (IPDS)

• IPDS automates the design of Instrument Flight Procedures (IFPs), and is a key component of the FAA Instrument Flight Procedures Automation (IFPA) program.

• IPDS supports multiple temporal statuses for each piece of data.

• User “pulls” data from distributed databases federated under a service-oriented architecture (SOA).

• IFP design is performed in local ‘Work Area’ that provides a spatial view of data.

• New and updated data is “pushed” back to FAA databases through web services.

4AIXM Users’ Conference, 18-20 March 2008

IPDS Aeronautical Data Interfaces

• FAA Service Providers expose aeronautical data through web services in an SOA that hides the actual database structure from the service users.

FAA Service Providers

Enterprise Service Bus

AIXM Web Services

AIXM Web Services

Web Services

ESB Service Directory

IPDS

FAA users

US Government Consumers

Aeronautical Charting

Flight Inspection

Publication Air Traffic

Airports

USNOF

PTS (Workflow)

Obstacles

Airports

SIAP (Approach

Procedures)

NAVAIDSFIX

(Designated Points)

US Government Service Providers

NGA

USGS

Future Web Services

5AIXM Users’ Conference, 18-20 March 2008

XSLT Used for Data Transforms

• On either side of each interface, AIXM transformation from / to internal representation is isolated to minimize the impact on the applications from changes to data exchange formats.

• On output, AIXM-5 is generated via XSLT transform on the internal model.

• On input, AIXM-5 is similarly transformed by an XSLT.

• XSLT selected over a data binding approach for:

• A smaller code base

• Agility to react to changes in data models on either side of the interface.

IPDS Application

Web Services Application

Logical ModelAirport

Database (Oracle

RDBMS)

Internal Representation

Mapping Layer

Web Service

AIXM XML SOAP

Message

AIXM to Logical Model (XSLT)

Logical ModelAeronautical

Database (Oracle XML)

Internal Representation

Mapping Layer

Logical Model to AIXM (XSLT)

6AIXM Users’ Conference, 18-20 March 2008

• Adopted a generic web feature service query model rather than defining individual and data specific queries, based on:

• OGC Web Feature Service (WFS) Implementation Specification• OpenGIS® Filter Encoding Implementation Specification.

• The model provides a generalized interface to all AIXM feature data:

• Consistent with OGC standards• Specified through a system-neutral query filter that can be transformed into SQL or XPath to fetch data.

• A generalized WFS request (getFeature) specifies: feature type, output format, and a filter to define scope of the query:

<GetFeatureRequest Encoding="UTF-8" CompressData="OPTIONAL"><wfs:GetFeature outputFormat="text/xml; subtype=gml/3.1.1 “ resultType="results" traverseXlinkDepth="0"> <wfs:Query typeName="aixm:AirportHeliport">

<ogc:Filter><ogc:BBOX><ogc:PropertyName/>

<gml:Envelope srsName="epsg:4326"><gml:lowerCorner>38.20527 -73.574472</gml:lowerCorner><gml:upperCorner>41.53861 -76.907805</gml:upperCorner></gml:Envelope>

</ogc:BBOX></ogc:Filter>

</wfs:Query></wfs:GetFeature></GetFeatureRequest>

Generalized Queries Using Industry Standards

Example Query by Bounding Box

7AIXM Users’ Conference, 18-20 March 2008

Generalized Queries Using Industry Standards

• The WFS implementation enables an allowable set of filter properties to query data by criteria:

• Spatial bounding box

• Country, State, Province

• Identifier and/or designator, with wild card queries

• Production status (e.g., active, pending)

• Effective date

• Last modified date.

• AIXM messages for spatial queries can be very large, so to reduce message size:

• XML response message are not indented (saves transmitting white space)

• XML response is compressed to reduce data transfer & memory requirements.

8AIXM Users’ Conference, 18-20 March 2008

AIXM 5.0 Extensions for IFP Design

• AIXM 5.0 does not support all FAA Instrument Flight Procedure design needs.

• The schema was extended using the AIXM 5.0 extensions model to support additional elements and capabilities:

• Production and Workflow elements• FAA-specific data elements for procedure design• Structured annotations on any feature by

extending the AIXM Note object• File metadata elements for the capability to

associate and store file attachments on any feature.

• Extensions are modelled in UML; and the XML schema generated by the FAA from the UML model.

VisualGlideSlopeIndicator

+ type : CodeVASISType+ posi tion : CodeSideType+ numberBox : NoNumberType+ portable : CodeYesNoType+ slopeAngle : ValAngleT ype+ minimumEyeHeightOverThreshold : ValDistanceVerticalT ype

(from Runway)

<<feature>>

VisualGlideSlopeIndicator

+ thresholdCrossingHeight : ValDistanceVerticalT ype

<<extension>>

FeatureExtension

+ productionStatus : CodeStatusProductionType+ workflowModel : CodeWorkflowModelT ype+ revision : TextDesignatorType+ lastUpdateDate : date+ lastUpdateBy : TextNameType+ stateT erritory : CodeStateTerri toryType+ country : CodeCountryType+ hostCountry : CodeCountryType+ sourceType : CodeSourceType+ surveyType : CodeSurveyType

(from Shared Feature Extension)

<<object>>

...

+featureExtension

...

extends

9AIXM Users’ Conference, 18-20 March 2008

Feature Identifiers and Associations

• Xlinks are a challenging aspect of AIXM 5.0:

• As a concept for the developers• In practice, for example accessing and navigating the XPath query

fragment in XSLT.

• The Xlink attributes are set in AIXM generation:

• The href is set to the XPath of the AIXM gml:identifier UUID of the referenced feature

• The title is set to the ‘natural key’ of the referenced feature, to provide a human-readable link that helps debugging.

<serves_RunwayDirection

xlink:href=“http://www.faa.gov/avnis?//aixm:RunwayDirectionTimeSlice

[../../gml:identifier[@codeSpace='http://www.faa.gov/avnis'] ='uuid0123' and (aixm:extension//dpshare:revision='2')]”

xlink:title = "//aixm:RunwayDirection//aixm:designator='27'

and //aixm:AirportHeliport//aixm:designator='KDEN'"/>

10AIXM Users’ Conference, 18-20 March 2008

Summary

• IPDS and existing FAA databases are successfully integrated using web services and AIXM 5.0 RC3.

• IPDS now provides browsing and querying FAA data sources in AIXM 5.0 format.

• Open industry standards used to simplify maintenance.

• AIXM 5.0 model was extended to support FAA IFP processes.

• Next IPDS release will extend the scope of AIXM 5.0 data exchange to include more feature types, data sources and the “push” of data into the distributed data enterprise

11AIXM Users’ Conference, 18-20 March 2008

Questions

MacDonald, Dettwiler and Associates Ltd.

http://www.mdacorporation.com/