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6 SOS Overview
6.1 General Approach
The goal of SOS is to provide access to observations from sensors and sensor systems in a standard way that is consistent for all sensor systems including remote, in-situ, fixed
and mobile sensors. This is a challenging task because the users of sensor data have historically been divided into those who primarily deal with in-situ sensors and those who
primarily deal with remote sensors. The terminology, perspective, and expectations of these two broad groups are different. SOS leverages the Observation and Measurements
OM specification for modelling sensor observations and the TransducerML and SensorML specifications for modelling sensors and sensor systems.
The approach that has been taken in the development of SOS, and the SWE specifications on which it depends, is to carefully model sensors, sensor systems, and observations in
such a way that the model covers all varieties of sensors and supports the requirements of all users of sensor data. SOS leverages the standard properties of these two data types
sensors, observations to provide specialized operation signatures for observation data.
This may be contrasted with the approach taken in the Web Feature Service WFS. WFS is based on a generic definition of a geographic feature that is flexible enough to
encompass any real-world entity, and uses GML application schemas to define the feature type exposed by a specific service instance. Hence, the WFS “get data” request is
highly parameterized since it must be fully generic. With this approach, interoperability requires organizations to agree on domain-specific GML application schemas. Clients
that access a WFS for rich processing in a particular domain must have a-priori knowledge of the application schemas used in that domain.
The SOS approach defines a common model for all sensors, sensor systems and their observations. This model is “horizontal” since it applies to all domains that use sensors
to collect data. The domain-specific details are encapsulated in the second layer features-of-interest, observed properties, sensor descriptions allowing the basic
“observation” to be processed by a generic client.
6.2 The Observation model