Review Comment:
The paper describes the SSN ontology, a recent recommendation by the W3C for modelling sensors and observations, and related data. The new version of SSN that is now also a W3C recommendation has some significant differences compared to the previous version, and in particular the recommendation consists of a set of different modules that build upon each other. For instance, SOSA is the core light-weight pattern for describing sensors and observation data, which is then imported by SSN that adds further axiomatization and extends SOSA in several ways. Additionally, there are also alignment modules, for instance aligning SSN to DUL, and modules for extending SSN in various directions.
As an ontology description paper I think that this paper would make a nice complement to the W3C documentation that is already online. As a W3C recommendation, the ontology obviously fulfils all the usual criteria, such as being accessible online, published according to good practices and with a stable URI, well-documented etc.
However, although the paper is well written and describes SSN in a reasonable and accessible manner, there is a bit of a lack of focus. What exactly is the scope of the paper? The title says "The SOSA/SSN ontology: ...", however, in the paper also other modules are described. It is not exactly clear if the name SSN should be interpreted as covering the whole family of modules or just the actual SSN module itself. If the former is intended, then that should be made more clear, and the reason for denoting both a module and the whole family of modules by the same name should be discussed explicitly, and if it is the latter then it is not clear why the authors chose to also describe several other modules in the paper.
Another issue, and perhaps the most difficult one, is that there is another paper submitted to the JWS, which is currently under review and where I have been one of the reviewers, that describes only the SOSA module separately. Although I clearly see that these two submissions are targeting two different audiences, i.e., since SOSA is a more light-weight vocabulary, and SSN is focusing more on axiomatization, the relation between the papers has not been made explicit. I do think there is sufficient need, and content enough, for two papers, but they need to be put in relation to each other. Since SSN imports and builds on SOSA, I do not see how one could publish a paper about SSN without at least introducing SOSA briefly, but the other way around works fine, since SOSA does not rely on SSN (other than on the old SSN as its origin). Hence, I would like to see this paper, targeting mainly SSN, referencing and building on the other paper, targeting mainly SOSA, for details regarding SOSA - just as SSN imports SOSA and extends it. In the current situation, however, this is impossible, since the other paper is still in review, and may be significantly changed in a revision process due to requests by the reviewers. This is the main basis for my recommendation for a major revision of the submission in question here, i.e., to allow for the other paper to become published before a revision of this paper is made. The reviewers can then also take into account this related paper (in its final form) when reviewing the revision of the paper at hand, and thereby more precisely judge the contribution and appropriateness of scope of this paper.
Some minor issues and questions:
- There are too many acronyms in the paper, some of which are very similar and can easily be confused (for instance O&M and OM, which denote two different things).
- Figure 1 is not clear and notation is not explained, e.g., what do the boxes encompassing several classes denote, and why the different colors? (Since I happen to have read the SOSA paper draft for JWS, there the explanation of these patterns is much better, hence, this would be a perfect place to, in addition to a clarification here, reference the other paper for more examples.)
- Would it be possible to give a joint overview of the examples/example scenario used in the paper in some kind of illustration? I recognise that the examples are online, however, in the paper the reader quickly notices that they relate to each other, but the reader also quickly looses the overview of what they are about. At least I think that they should be numbered so that they can be uniquely referenced in the text. As it is now they are referenced by section, which is not very precise, and sometimes references even seem to be wrong (e.g., on page 7 the authors refer to the example in section 4.2, but there is no example there, potentially they mean 3.2).
- Figure 3 seems quite meaningless without any content in the respective boxes. Remove or detail the illustration.
- Second paragraph in section 5 starts with "It" but it is not clear to what ontology this refers.
- There is some confusion around the focus of various modules it seems. In the third paragraph of section 5, page 6, the core component (of SOSA/SSN?) is claimed to focus on three perspectives: sensor, actuator, sampler, and section 3 is referenced for explanations of these. Although I can see these three concepts in Figure 1 in section 3, the main structure of section 3 instead seems to focus on observations, sampling and actuation. Since I already read a lot about SSN, and the patterns in there, I can understand that these things actually refer to the same three patterns, but another reader may not be so lucky. I suggest the authors select one name for each pattern/perspective, and stick to it throughout the paper.
- What does "certain communities" refer to in the last sentence of 5.1?
- First section of 5.2: what exactly is the kind of property that you refer to as an OWL/RDF property?
- First sentence of second paragraph in 5.2.3 seems strange.
- The acronym QUDT is introduced in 5.4.1 but it has already been used earlier in the text.
- Last sentence of the second paragraph in section 8 (on page 16) is unclear.
- I assume you mean SSNX at the beginning of the first sentence, second paragraph, of conclusions section.
- Some references in the references section are incomplete. In particular many of them lack a publisher, e.g. when referring to proceedings books. Some also lack a volume number, such as when referring to CEUR proceedings. [38] has a last accessed date but no URL.
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