Vocabulary for sensor networks: W3C SSN Ontology

The Semantic Sensor Network Ontology (SSN) is an ontology that describes sensors and observations, that is, the physical data measured by devices. This vocabulary is intended to play a crucial role in the application of semantic technologies in application areas related to Smart Cities and the Internet of Things (IoT) and, therefore, has potential uses in many domains, for example, for environmental control issues (air and water quality), precision agriculture, traffic management, integration of health control processes, etc.

The SSN ontology is an OWL vocabulary developed by the W3C in collaboration with the Open Geospatial Consortium (OGC) to define a general standard for describing sensor networks aligned with Semantic Web technologies and the Linked Data paradigm. It is currently in the ‘Working Draft’ phase, as of the 4th of May, 2017. Given the multitude of scenarios and use cases of this ontology, its design is based on a modular architecture (horizontal and vertical) that allows it to be organically extended on the basis of a minimal common vocabulary. This vocabulary has been designated SOSA, according to its main concepts:

1.   Sensor: devices that measure one or more physical magnitudes: for example, accelerometers, gyroscopes, barometers, etc.

2.   Observation: the actual or estimated value of a physical magnitude.

3.   Sample: representative samples of a given magnitude.

4.   Actuator: a device that modifies physical quantities based on instructions, such as a fan or door operator.

The following diagram illustrates this modular design of the SS ontology:

Source: SOA and SSN ontologies with their respective modules. W3C

One of the most noteworthy aspects of this SSN ontology is, as has been mentioned, the participation of the OGC as an integral part of the process. This means that the final version of the document will be a joint standard of the two organisations: W3C and OGC. Furthermore, work has been done on the compatibility of SSN with existing OGC standards for the annotation of sensors and observations. Namely, with:

·         OGC Observations and Measurements standard. XML vocabulary for the description of the conceptual model of Observations and Measurements (O&M) for the publication of environmental observations, published jointly by the OGC and the ISO (in this case as ISO/DIS 19156).

·         OGC Sensor Model Language (SensorML). XML vocabulary to describe sensors, actuators, as well as the procedures to measure and transform observations.

In the coming months, contributions and revisions of this first definition of the standard are expected at the international level, as well as reference implementations that will enable the next phase of the vocabulary standardisation process. In particular, broad participation is expected from the realm of open data and especially from projects linked to the development of the Smart Cities concept.