ETF WSN Testbed: Practical Health Enhancing Application of Wireless Sensor Networks - Application and Multidisciplinary Aspects of Wireless Sensor Networks - page 252

Usually, at the beginning of communication the client sends to the PCG server a
login request, and after receiving login confirmation requests for getting meta-
definitions, and sensor network object where this client belongs. After this initial
message exchange, the client is ready to send either requests for registration of new
sensors, or to notify the PCG server with the latest sensor observations. The client
PCG package contains some utilities classes that facilitate creating of appropriate
sensor observation transfer object for a certain sensor. This sensor observation
transfer object is needed for notifying the PCG server with latest observations
from sensors.
All Internet users are potential users of PCG service. A demonstration application
is developed (see Fig. 12.1 above) for showing possible modes of using PCG capa-
bilities. There are several use cases. User can manually discover which sensor net-
works are connected to the PCG. For each sensor network, there is a list of sensors
deployed in that sensor network. If location property for those sensors is provided,
users can see on the map where that sensor is deployed by clicking on the sensor in
the list. Another possibility for users is to search for some sensor data using temporal,
spatial, and values filters. Temporal filters apply on sensor observation, with the
possibility of selecting observation in some time interval, after some time, before
some time, or just latest gathered observations. Spatial filters are used for selecting
sensors from some area. This area could be determined using the map, and there is
an option of box area, or polygonomial area. Values filters are offered if user selects
searching by some sensor type. Based on appropriate meta-sensor, several properties
could be included in search criteria, as a condition with desired values that observa-
tions from sensors must satisfy. After submitting queries to the PCG, user receives
response as a list of sensor observations or sensors that satisfy the query. Gathered
sensor observations could be browsed using the map or using the list. User can also
get history of sensor observations for selected sensor. Additionally, user can sub-
scribe for receiving the latest observation for selected sensor and automatically display
it using the table or graph (Fig. 12.7 ).
Fig. 12.7 Sensor data acquistion through the PCG