Sensor Networks’ Integration - Application and Multidisciplinary Aspects of Wireless Sensor Networks - page 98

applications. The current standards framework encompasses seven different
standards, some of them completed and others in draft stage. Three of the standards
are concerned with the XML-based encoding and representation of sensor informa-
tion/observations and the description of sensor capabilities and related information
processing steps. The remaining four standards describe standard web service inter-
faces for tasking of and interaction with sensors. The observations and measurement
( O&M ) schemas provide XML schemas for representing and observations, mea-
surements, procedures, and metadata of sensor systems and efficiently encoding
them for transfer and archiving. The sensor model language ( SensorML ) supports
the description of a functional model of a sensor system by providing models and
XML schema for describing processes of measurement and post-measurement pro-
cessing and their exact chaining. The transducer markup language ( TML ) provides
models and CNK schema for describing hardware response characteristics of trans-
ducers (more complex integrated sensors/actuators) and efficient method for encoding
and real-time transport of sensor data. While partially overlapping with SensorML,
TML focuses more on support of streamed real-time sensor information flows,
preserving their spatial and temporal association for later data fusion. The sensor
observation service ( SOS ) specifies a web service interface that allows SWE clients
to obtain observation and measurements from a collection of sensors. The SOS also
allows clients to access metadata information about associated sensors, platforms,
procedures, and other metadata associated with observations. The information is
exchanged using the three aforementioned XML-based data formats. The sensor
planning service ( SPS ) acts as a broker service between clients and different SOS.
It allows clients to determine the availability of certain sensing services that may be
needed to satisfy collection requests and the feasibility of those via a standardized
web service interface, potentially spanning multiple sensor systems and manage-
ment of such collection requests. The sensor alert service ( SAS ) provides web ser-
vice interfaces that allow clients to subscribe to alerts/event notifications of
particular sensors. The SAS acts only as a registry that enables clients to determine
the nature of available alerts, protocols used, and the options to subscribe to specific
alerts. Alerts or event notifications themselves are forwarded my messaging servers.
The web notification service (WNS) specifies a web service interface that allows
clients to interact with one or more services in an asynchronous way. WNS provides
support for both unidirectional and bidirectional asynchronous communication.
The standards framework of SWE addresses many issues including standardized
descriptions for sensor/actuation platforms, actual sensor information and processing
chains in a sensor web as well as several interfaces for applications to interact with
sensor systems, perform asynchronous communication, and manage event notifica-
tions. In addition the SWE framework defines interfaces for a service-broker-like
component, the SPS, which enables more complex interactions between applica-
tions and sensor systems, such as determining suitable sensor observation compo-
nents across multiple sensor systems and information repositories to satisfy more
complex sensing requests and the respective tasking of the sensor systems. While
specifying the high-level architectural framework and interfaces, the SWE does not
address the realization of the framework services or required interaction protocols.