Need to represent measurements with more than one value and values without unit of measurement
In the COGITO Project we have found a couple of requirements that are currently not being covered by the SAREF ontology.
In construction sites there are tracking devices for workers and equipment that track the location of these resources. The result provided by these devices is a point in space with the location of the resource.
Right now SAREF expects that every measurement has as a result exactly one value (since the range is not defined for saref:value, this is not a problem since the value could be a point) but SAREF also requires that every measurement has exactly one unit of measurement. In this case, since points do not have a unit of measurement, they cannot be directly represented in a consistent way.
Furthermore, the tracking devices can provide different values for the same measurement, such as the point directly measured by the device or the point after applying some filtering (e.g., Kalman) to improve the accuracy of the measurement. Since SAREF requires having exactly one value as the result of a measurement, this situation cannot be represented in SAREF.
In the COGITO IoT ontology (https://cogito.iot.linkeddata.es/def/iot#) we have partially solved the issue by creating a new class Result and a property hasResult that links the Measurement with a Result. But the restriction on the unit of measurement is still there.