Review Comment:
This survey paper focuses on reviewing different ontologies as KR formalism for streaming linked data (SLD). Three perspectives are considered: the suitability of a given ontology for SLD as web resources, assessed based on FAIR principles; ontologies used for describing stream structure, assessed based on metadata and reasoning capability of such ontologies with respect to Stream Reasoning tasks; and ontologies for the stream content, assessed based on the suitability of the representation to characterise event patterns.
The topic as well as the need for the proposed survey is suitably presented, minor some imprecisions, and there is a clear indication of how the selected approach to compare have been identified.
The focus is on the ontological side of things and RDF Stream Processing, and does not cover other expressively levels of stream reasoning such as CEP or non-monotonic stream reasoning. This has been somehow mentioned at the beginning, but it should be clear that this survey specifically targets approaches to RDF Stream Processing, a subset of Stream Reasoning research.
The more general definition of SR as an area of research, however, is provided in the Encyclopaedia of DB Systems [1] and should be referred to when talking about SR research.
[1] Mileo, A., Dao-Tran, M., Eiter, T., Fink, M. (2018). Stream Reasoning. In: Liu, L., Özsu, M.T. (eds) Encyclopedia of Database Systems. Springer, New York, NY. https://doi.org/10.1007/978-1-4614-8265-9_80715
BALANCE ACROSS THE THREE PERSPECTIVE (streams as web resources, stream structure and stream content):
There are a few gaps in the analysis and discussion:
- R3 is not covered in table 3 and discussion.
- At the end of Section 4 here is an intuition on the combination of some ontologies to maximise coverage of FAIR based on Table 3. However it is not clear what are the point of contact/integration or via which specific concept can the combined ontologies overlap and whether these can be used to guide the selection of which ontologies to integrate.
- SSN/SOSA L4 missing from Table 4 but present in text
- comments about the Composition of events says that this is not discussed at the level of Section 6 as can be defined at higher levels of abstractions. However, there is no discussion of the composition/reasoning capability of the ontologies used at the structure level (Which is where I suspect the composition might occur?)
I think the ability to reason over streams structure (Section 5) is lacking some more formal specification of the properties of each meta-structure Level, as well as a discussion of the expressivity of the related ontologies. Shouldn’t the ability to do (stream) reasoning at this level be considered and compared as well? Independently of the type of concepts used for representing the meta-structure of streams, the semantic of those is greatly embedded in the ontology’s expressivity and reasoning capability.
The survey paper is presenting an interesting analysis of different ways for representing and manipulating Linked Stream Data in RDF, and can be valuable as a guide for the research community working in this area specifically. What is missing, however, is a set of best practices or use-case scenarios that would indicate the suitability (or not) of some specific ontologies across all three levels discussed in the paper.
I would suspect that in some cases ticking all the boxes at one level might be more relevant even though other levels are not entirely covered.
This would be a very valuable addition to the Survey and could, in this instance, be achieved by characterising research paper that have used a specific type of ontology/ontologies to represent and process LSD.
Sharing code not applicable to this survey type article
Comments on Clarity:
It is not clear whether the identification of the three perspectives happened before the paper selection process, or was determined by the result of the paper selection process. Please clarify.
Improvements could be made re. Readability and clarity, specifically with respect to some common imprecisions in the text overall. Details as follows:
You need to check for typos and grammatical errors throughout
Some words are strike-through to indicate those aspects have not been considered in the paper. This is not the way to indicate that.
Page 2: “A number of worked emerged…” (missing references)
Page 2: Incomplete sentence: “Event though a number of … applications. ”
Ref [15] is incomplete
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