Definition and Subscription of Events

SANY D2.3.4 Specification of the Sensor Service Architecture V3 Doc.V3.1 Copyright © 2007-2009 SANY Consortium Page 219 of 233 that allows message delivery to any form of communication endpoint, but lacks a number of security and maintenance features. Figure 10-30: Event handling using OGC Sensor Alert Services In the following, we will illustrate the principle modes of operation of SAS as used in SANY. Events can be discovered at various levels, for example by sensors themselves, or during processing of reported observation data by the Sensor Alert Service. The following figures illustrate the various cases.

10.11.1 Definition and Subscription of Events

Initially, two scenarios must be differentiated, as illustrated in Figure 10-31 and Figure 10-32. Figure 10-31 illustrates the simplest scenario. Sensors define events and advertise them to an SAS instance. Those event-types will then be advertised by the SAS. Clients can subscribe to those events exclusively. As an example, the sensor triggers events if the temperature exceeds 10 °C. The clients can subscribe to “temperature exceeds 10°C” exclusively. Other commonly used examples of predefined events are “battery low” or “observation failure”. . Figure 10-31: Clients subscribe to sensor-defined event types Figure 10- 13 illustrates the second scenario. Sensors don‟t define event-types, but advertise observation data to the SAS. SAS will advertise these data to clients. Clients are now free to define their own events based on the observation data. As an example, a sensor offers SANY D2.3.4 Specification of the Sensor Service Architecture V3 Doc.V3.1 Copyright © 2007-2009 SANY Consortium Page 220 of 233 temperature observations at a certain location in degree Celsius. The client may define an event as an observation with a result greater than 20°Celsius. Figure 10-32: Clients define events based on observation offerings by sensors or SAS respectively The next scenario, illustrated in Figure 10-33, describes a combination of the two base types described above. Here, a single sensor or any number of sensors push data to the SAS instance. Independently of the type of incoming data either observation results or event notifications, the SAS instance may define and advertise new event-types. Clients can then register those event-types. The SAS will process all incoming data to detect the type of event it advertises. An example would be an SAS that advertises “storm warning” events. The “storm warnings” are detected based on data coming from a number of meteorological sensors. Figure 10-33: SAS defines event types based on various incoming data sets. Clients subscribe to those events

10.11.2 Generation and Dispatching of Alerts