Web Feature Service Event Service

Copyright © 2011 Open Geospatial Consortium. 11 Figure 5-2. SAA Pilot Study OGC Components

5.1 Web Feature Service

A WFS OGC 09-025r1 is a stateless requestresponse web service involving XML messages encoded using a GML application schema such as AIXM 5.0 or AIXM 5.1. The WFS supports HTTP GETPOST or SOAP bindings. The WFS is analogous to existing SAA requestresponse services but provides a more comprehensive set of operations and querying capabilities. These WFS 2.0 operations allow clients to discover, access and maintain data within a remote data store. The stored query operations, new to the WFS 2.0 specification provide significant benefits as WFS administrators can pre-define common complex queries that can reduce implementation barriers for client application development. Query operations are underpinned by the OGC Filter Encoding 2.0 specification OGC 09-026r1 that defines a set of filter expressions that enable fine-grained retrieval of data via any OGC web services. The WFS query operations also allow clients to perform: Single or multiple queries Join queries optional: property, spatial, temporal Resolve: to include referenced features in the response Coordinate reference system transformation optional Define how the response is returned: Sort order or alternate response hits = number of features corresponding to query Exclude unwanted optional properties in response 12 Copyright © 2011 Open Geospatial Consortium. The WFS enables users to perform a wide range of queries from simple queries: Get me all features within a bounding box Get me the Airspace with the identifier: eafcbdff-e8cc-4afd-beb3-3c08883b7b1d to more complex queries: Get all active Airspaces within 200 nautical miles of a route Get the names of all military Units operated by US Navy

5.2 Event Service

As part of the OGC Web Services OWS initiative, the OGC has developed a service specification for event notifications based on the OASIS Web Services Notification standard. An Event Service allows users to automatically receive notifications about feature-related events, which represent updates to feature property values state changes. This is analogous to the asynchronous SAA Service publishsubscribe pubsub topics implemented using the Java Messaging Service JMS standard, but without vendor-specific JMS binding issues. In addition, the Event Service subscription can include filter criteria for pre-defined event topics as well as filters that operate on the spatial, temporal andor thematic properties of events, much like the WFS filters. Details on the Event Service implementations used in the Pilot Study can be found in section 7.1. The encoding of the events used in the Pilot Study is also described in section 7.1. The Event Service design also includes a standard “heartbeat” channel to allow subscribers to confirm the continuing availability and connectivity to the Event Service see section 8.8.

5.3 Event Service Adapter