5 Introduction to OGC SensorThings API

The SensorThings API (STA) is a standard of the Open Geospatial Consortium (OGC). It provides a framework for communication and exchanging data between sensors and applications. The standard is devided in two parts. SensorThings API Part 1 is dedicated to sensing and was published in 2016 and updated in 2021.
A STA-based architecture works in client/server mode. A sensor device pushes data to the SensorThings Server via HTTP. A SensorThings Server may also support MQTT protocol to support publish and subscribe capabilities. An interested application can subscribe to the MQTT-Broker, in order to get notified about new sensor events.

Figure 5-1 STA message flow

The data in the SensorThings server are organized as according to Sensing Entities (see Figure 5-2: Sensing Entities data model.

Figure 5-2 STA Sensing Entities Data Model

In the Sensing Entities Data Model events or sensor data are called "observations". Before a sensor is able to push an observation to the server it needs at least a 'Thing' and a 'Datastream' entity. This has to be created beforehand. One 'Thing' might have different 'Sensors', one 'Location' or many 'HistoricalLocations'.

The Sensing Entities data model and the purpose of data within the data model discloses mainly two data characteristics, associated with a 'thing': - Data observations originated by sensors or commands sent to interact with actuators may be seen as IoT data from oneM2M point of view. While: - Data embedded in the Sensing Entities Data Model, like "historic locations" should be seen as data for documentation purposes.