The Modular SSN Ontology: A Joint W3C and OGC Standard Specifying the Semantics of Sensors, Observations, Sampling, and Actuation

Tracking #: 1878-3091

Armin Haller
Krzysztof Janowicz
Simon Cox
Maxime Lefrançois
Kerry Taylor
Danh Le Phuoc
Josh Lieberman
Raúl García-Castro
Rob Atkinson
Claus Stadler

Responsible editor: 
Pascal Hitzler

Submission type: 
Ontology Description
The joint W3C (World Wide Web Consortium) and OGC (Open Geospatial Consortium) Spatial Data on the Web (SDW) Working Group developed a set of ontologies to describe sensors, actuators, samplers as well as their observations, actuation, and sampling activities. The ontologies have been published both as a W3C recommendation and as an OGC implementation standard. The set includes a lightweight core module called SOSA (Sensor, Observation, Sampler, and Actuator) available at:, and a more expressive extension module called SSN (Semantic Sensor Network) available at: Together they describe systems of sensors and actuators, observations, the used procedures, the subjects and their properties being observed or acted upon, samples and the process of sampling, and so forth. The set of ontologies adopts a modular architecture with SOSA as a self-contained core that is extended by SSN and other modules to add expressivity and breadth. The SOSA/SSN ontologies are able to support a wide range of applications and use cases, including satellite imagery, large-scale scientific monitoring, industrial and household infrastructures, social sensing, citizen science, observation-driven ontology engineering, and the Internet of Things. In this paper we give an overview of the ontologies and discuss the rationale behind key design decisions, reporting on the differences between the new SSN ontology presented here and its predecessor developed by the W3C Semantic Sensor Network Incubator group (the SSN-XG). We present usage examples and describe alignment modules that foster interoperability with other ontologies.
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Solicited Reviews:
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Review #1
By Alessandro Oltramari submitted on 11/May/2018
Review Comment:

The authors' response has carefully addressed the issues pointed out in my review. The paper has been modified accordingly. Overall, I think that the article has been substantially improved from the original submission, gaining in clarity of scope, and improved in the quality of the ontological analysis.
I'm in favor of accepting it for publication.

Review #2
By Eva Blomqvist submitted on 11/May/2018
Minor Revision
Review Comment:

I would like to thank the authors for the thorough revision of the paper, which addresses most of the comments in my previous review. The scope of the paper is more clear, the figures are better explained, terminology has been sorted out and unified, and so on. However, there are still a few improvements needed.

Regarding the discussion concerning the related submission to the Journal of Web Semantics, the situation here is still not entirely clear. Since that paper is still being reviewed/revised, one can only rely on the authors assuring that the papers will not contain a considerable overlap. I thank the authors for providing the latest version of the other paper for comparison, but since it might not be the final version it is still hard to assess the final relation between the papers. Nevertheless, the authors now provided a reference to the other paper inside this submission, which was one of the major things required. I would however suggest to wait until the other paper is also accepted and published, so that a stable reference can be provided (rather than the current "under review" one). This is my main reason for selecting "minor revision" rather than "accept" as an overall recommendation. Additionally, that paper is now only referenced in one single place (section 1, page 2). I would like to see it referenced in more places, i.e., all places where SOSA is mentioned in passing and where the reader could benefit from a pointer where they can find more explanations about SOSA.

Additional minor issues:

- O&M is first mentioned on page 2, but there without any explanation or reference. Only later comes the explanation of what it is, how it relates to SSN and references where to find it.

- There is still a bit of a mix between referring to the old version as the "original SSN" or SSNX. Terminology could be refined even further here. The same goes for usage of "new SSN" versus "SOSA/SSN" - are these synonyms, or do you mean different things when writing these?

- Thank you for adding Figure 2, I think it gives the needed overview of the example that I asked for. However, the notation is not correctly described in the caption. Since dashed boxes are instances and black ones are classes, I assume that you mean the solid lines are rdf:type rather than "is a relations" as the caption says?

- I assume that the appendices mentioned on page 19 are actually the three tables located on the following pages (mixed with the reference list). Either these should be made into appendices, located after the reference list, or they should be mentioned in the text as tables instead.