Problem Statement Concept and Methods Implementation

70 Copyright © 2013 Open Geospatial Consortium. metadata as requested by the client e.g. via an appropriate parameter in a WFS-T 2.0 GetFeature request or in an ES subscription.

7.4.6.1 Problem Statement

Metadata is encoded in properties on message, feature or time slice level. As ordinary properties, metadata elements are always returned inline together with the other contents of a feature. Some applications might not process metadata at all and, as it might be huge in size because of its verbosity, clients should be able to request it on demand. This is not covered by the WFSFES standards.

7.4.6.2 Concept and Methods

The goal was to provide a method for the client to request feature data without metadata. This can be achieved by the introduction of a projection clause. In the WFS Temporality Extension, the PropertyExclusion projection allows the client to specify elements to exclude from a response by an XPath expression. If the XPath points to the metadata elements to remove, the requirement is fulfilled.

7.4.6.3 Implementation

For WFS servers the implementation of this feature is described in the WFS Temporality Extension ER,[OGC 12-146 ]. As the Event Service Subscribe request only uses the “Filter” element of FES no direct support for FES projection clauses was available. Therefore, an extension schema for the Subscribe method was developed to provide a similar semantic and syntax as used in the WFS implementation. Listing 10 illustrates an encoding of a subscription with a PropertyExclusion projection defined. The schema for the FilterWithProjectionClause element is attached to this document see Annex B. Listing 10 – Example Metadata Exclusion Subscription. wsnt:Subscribe wsnt:ConsumerReference wsa:Address {consumer} wsa:Address wsnt:ConsumerReference wsnt:Filter xmlns:aixm = http:www.aixm.aeroschema5.1 xmlns:wsnt = http:docs.oasis-open.orgwsnb-2 wsnt:MessageContent Dialect = http:www.w3.orgTR1999REC-xpath-19991116 xmlns:xlink = http:www.w3.org1999xlink aixm:Runway wsnt:MessageContent wsnt:MessageContent Dialect = http:www.opengis.netsesfilterlevel2 es-pc:FilterWithProjectionClause xmlns:gmd = http:www.isotc211.org2005gmd xmlns:fes-te = http:www.opengis.netfes- te1.0 xmlns:es-pc = http:www.opengis.netes-pc0.0 fes-te:PropertyExclusion fes-te:propertyName aixm:featureMetadata fes-te:propertyName fes-te:PropertyExclusion fes-te:PropertyExclusion fes-te:propertyName aixm:timeSliceMetadata fes-te:propertyName fes-te:PropertyExclusion es-pc:FilterWithProjectionClause wsnt:MessageContent wsnt:Filter wsnt:Subscribe Copyright © 2013 Open Geospatial Consortium. 71

7.5 Service Discovery Based on Spatial Extent

Within the scope of service discovery an additional goal was the capability to identify services which provide data for a certain spatial extent e.g. Europe, US. For WFS instances this is achieved by providing an ows:BoundingBox for every item in the FeatureTypeList. As an ES theoretically can take any data as an input it naturally does not have a spatial limitation. To support discovery based on the spatial extent, the WFS’s integrated an additional Capabilities element to point to the ES endpoint where DNOTAMs are sent to see Listing 11Error Reference source not found.. This way, the registry is able to map the ES instances to the WFS instances, hence providing discovery by spatial extent. Listing 11 - Exemplary Event Service Reference for the IfGI ES. ows:ExtendedCapabilities es:EventServiceReference es:Publisher es:serviceNameSesServicees:serviceName es:WSDLhttp:v-tml.uni- muenster.de:8080EventServiceservicesBroker?wsdles:WSDL es:Publisher es:EventServiceReference ows:ExtendedCapabilities

7.6 Accomplishments

Within this OWS, several new aspects and features which improve the data provision services were designed and implemented. Most of these new features were designed to make the life of clients using these services easier e.g. the introduction of Stored QueriesFilter into the Aviation architecture, “AIXM Features as Geometry Operands” as well as “Spatial Filtering on Non-spatial Features”. Additionally, a special focus was laid on performance and bandwidth improvement. This has been achieved for instance by defining the explicit exclusion of metadata when receiving data on AIXM features but also through the introduction of “feature provision by reference” through the gml:identifier and the design of “Update Intervals” for Event Service subscriptions. The latter also helps a client e.g. a pilot to focus on the most relevant information. In contrast to previous OWS test beds efforts on creating filters which take the vertical extent of features into account have been made. In particular, the design of simple altitude queries forms a valuable basis for future scenarios which require the filtering based on altitude limits.

7.7 Lessons Learned

Taking the vertical extent of AIXM features into account when applying filtering has been identified as a challenging task. Especially when dealing with complex Airspace geometries or three-dimensional flight routes a simple approach was not sufficient. The work on altitude queries improved the overall comprehension on complex AIXM features and is reflected in a matured filtering capabilities.