Data Provision Eventing Components and Dataflow

58 Copyright © 2011 Open Geospatial Consortium, Inc. All Rights Reserved. and act as WS-N Publishers. Such events are pushed to the Event Services when they become available at the WFSs. The WFS servers also act as a static repository for retrieval of AIXM features and snapshots as described in section 9.5.1. Listing 3 – Example digital NOTAM Notification Listing 3 populates a “Navaid unservicable” DNOTAM using a Tempdelta. It uses the NavaidExtension to link to the Event feature contained in the same XML document.

9.3.3 Data Processing

The actual processing is done by the Event Services. All incoming digital NOTAMs are checked against subscriptions more specifically: the filters they define created by the clients. If a filter matches for a certain subscription the originally received DNOTAM is pushed to the client without modifying it. This must also be the case if the Event Service applied enrichment of thin events see section 9.5.1.

9.4 Dynamic Filtering

The OWS-7 Aviation Architecture Engineering Report OGC 10-079, Section 8.4.5 introduced the concept of a dynamic filter for DNOTAM events. During OWS-8 the wsnt:Notify xmlns:wsnt=http:docs.oasis-open.orgwsnb-2 wsnt:NotificationMessage wsnt:Message msg:AIXMBasicMessage gml:id=gmlID14726 xmlns:msg=http:www.aixm.aeroschema5.1message xmlns:gml=http:www.opengis.netgml3.2 xmlns:aixm=http:www.aixm.aeroschema5.1 xmlns:dnotam=http:www.aixm.aeroschema5.1event msg:hasMember dnotam:Event gml:identifier codeSpace=urn:uuid:BCB4F904-9AEA-4F2E-97AE- 2D4A4344BD6Cgml:identifier dnotam:timeSlice ... dnotam:timeSlice dnotam:Event msg:hasMember msg:hasMember aixm:Navaid gml:id=gmlID14730 gml:identifier codeSpace=urn:uuid:BCB4F904-9AEA-4F2E-97AE- 2D4A4344BD6Dgml:identifier aixm:timeSlice aixm:NavaidTimeSlice gml:id=gmlID14731 ... aixm:interpretationTEMPDELTAaixm:interpretation aixm:sequenceNumber1aixm:sequenceNumber aixm:correctionNumber5000aixm:correctionNumber ... aixm:availability aixm:NavaidOperationalStatus gml:id=gmlID14734 aixm:operationalStatusUNSERVICEABLEaixm:operationalStatus aixm:NavaidOperationalStatus aixm:availability aixm:extension dnotam:NavaidExtension gml:id=gmlID14735 dnotam:theEvent xlink:href=urn:uuid:BCB4F904-9AEA-4F2E-97AE- 2D4A4344BD6C dnotam:NavaidExtension aixm:extension aixm:NavaidTimeSlice aixm:timeSlice aixm:Navaid msg:hasMember msg:AIXMBasicMessage wsnt:Message wsnt:NotificationMessage wsnt:Notify Copyright © 2011 Open Geospatial Consortium, Inc. All Rights Reserved. 59 details for such a concept have been developed and implemented prototypically. Figure 22 illustrates the idea of this concept. Figure 22 – Dynamic buffer of a flight route As illustrated in this example a client receives a notification about the activation of an Airspace Time B. Later Time C another Airspace is activated and the formerly activated Airspace gets inactive again. The clients do not receive notifications for these events as the buffer used as filter geometry is updated dynamically using the position updates received by the aircraft. By updating a dynamic subscription using position data a client does not have to manage multiple subscriptions for each route portion and no further requestresponse communication to update the filter geometry is needed. In addition, another advantage of such a subscription is that no unnecessary information is delivered to the clients. Hence bandwidth is not wasted and the pilot or dispatcher is not distracted by irrelevant DNOTAMs.

9.4.1 Creation of a Dynamic Spatial Filters

The support for dynamic subscriptions in the Event Service in general can be realized using the Event Pattern Markup Language EML. EML is currently a discussion paper at OGC OGC 08-132 and several improvements happened to it since its submission. The concept is based on Complex Event Processing CEP to define patterns of Events.