Ontology Engineering: Current State, Challenges, and Future Directions

This is a relevant paper for this call, which aims at summarising the current state of the ontology engineering field in the last decade. Indeed, it is also very related to another paper that has been submitted to the same call, where a list of the main challenges for ontology engineering in the current state of the art is also addressed, from a point of view of the main functionalities that need to be addressed in that context.

I really like the first part of the paper, section 1, which aims at providing an overview of how ontologies have had an impact in the state of the art in different domains. It is true that it is difficult to make a thorough comprehensive analysis of all areas that have really benefited from teh use of ontologies, given the wide range of cases and domains that are using them, but the selection provided by the author is really representative. I would probaably only add some examples from the geographical domain (there are ISO standards that are also proposing the use of OWL ontologies for the representation of geographical features).

The description of recent standards is also accurate and I do not recall any other standard that may be added here, taking into account the retrospective on the last 10 years.

When we move into the large-scale community driven creation of knowledge, I am clearly missing the work done on DBpedia, which should not be overloooked, even if initiatives like Wikidata are taking over much of the work that was done there. Indeed, the focus in that section is too much on the data itself, which is always accompanied by ontologies, but there is not so much discussion on the different ontology engineering efforts that are done around those community-driven efforts. Also other ontologies associated to these efforts, like YAGO, or work that has been done around all these resources, may be relevant in this analysis, so that it is not too strongly biased on only a few cases.

Finally, when we move into section 4, on ontology engineering, I think that the author has also tried to cover the most relevant cases where work on ontology engineering has been done, both on methods and tools. I would have appreciated a more critical approach as to whether any of these methods or tools are actually doing it right. Are there any lessons learned from the application of the NeOn methodology? Is there anything different from industrial settings when compared with academic settings in terms of ontology development tool support?

Finally, the challenges section is the one that I am not so convinced of. Indeed, if one would read only the bold font in that section, it may seem that all the challenges are around usability of ontology engineering tools and methods, modelling challenges and the need for better training. Is it really the only reason why ontologies are not widely adopted by a stronger/larger user base? Why is it really teh case that software developers are still creating their own JSON schema files to describe their JSON models instead of adopting a more comprehensive and formal approach for the representation of those schemas? Why is it the case that schema.org is using domainIncludes and rangeIncludes and only stays at a very superficial/lightweight way of modelling? These are aspects that IMO are not sufficiently covered in this paper, and where the experience of the author may shed some light. Nothing is said about the importance of SKOS thesauri in collaborative ontology development, especially when it comes to getting quick agreements before going further in the representaiton of a domain. I think that further thought into these aspects and more clear recommendations of the next steps to be taken for ontology engineering in this new setting may make the paper more useful. As a developer of some tools mentioned in this paper, as well as new methods for otnology development, I would really like to be challenged with clear views of where we should go into in 10 years-time.

In any case, I think that this is a valuable contribution for this special issue, which brings in a lot of experience gathered on supporting ontology engineering in a range of domains for a large number of years.

The article is an overview of the state of the art in Ontology Engineering (OE), with a focus on the last ten years, and proposing some areas of improvement.

The contribution is well written, and summarizes a representative sample of the work carried out in OE. From my perspective, a few additions/clarifications would make the overview a better one (see list below).

My main criticism concerns the scope of the "challenges and opportunities for future research", which is quite generic, and sounds like a project report rather than a research-oriented vision statement (as these SWJ issues typically encourage). My suggestion here is to figure out new methods and hybridisations, which could make a breakthrough.

Additions/Clarifications for the overview part (sections 1-4):

1) some mention of advancements in formal ontology, at least in their applications to the SW. As an example, [1] shows the power of a foundational ontology in discovering anti-patterns and inconsistencies in a large knowledge graph such as DBpedia

2) although not comprehensive, the mentioned domains sampled in the overview should be representative. This is not the case with cultural heritage, whose state of the art sampling is limited: "In the cultural heritage field, the ISO 21127:2014 standard prescribes an ontology that allows the exchange of cultural heritage data between institutions, such as museums, libraries and archives". However, much work has been done, spanning from Eero Hyvonen work to FRBR, Europeana, and the recent advanced ontology network (ArCo) used to design the huge knowledge graph of Italian Cultural heritage [2]

3) in the methodological part, eXtreme Design [3] is missing, despite its focus on design pattern-based iterative design without using waterfall, usually rigid methods that are widespread in the literature

4) ODPs are referenced through a couple of publications, and its workshops, but not with its repository [4], which is essential for the community, originally bootstrapped in the NeOn project (mentioned elsewhere), but still actively used after more than 10 years

5) Widoco ontology documentation tool is mentioned, but that style of documentation has been initiated by LODE [5], and actually reused in Widoco

6) the Gra.fo tool is mentioned, but not the original inspiration for this kind of viz tools, i.e. VOWL [6], and its set of tools, e.g. WebVowl [7]

7) some important sub-areas of OE are under-represented: ontology matching, reuse, evolution, learning. This is true both for the overview, and the challenges/opportunities parts

8) A citation is incomplete:
[37] P. Hitzler, A. Gangemi and K. Janowicz, Ontology engineering with ontology design patterns: Foundations and applications, Vol. 25, IOS Press, 2016.
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[37] P. Hitzler, A. Gangemi, K. Janowicz, A. Krishnadi, V. Presutti, Ontology engineering with ontology design patterns: Foundations and applications, Vol. 25, IOS Press, 2016.

[1] Experimenting with eXtreme design, ISWC2015
[2] ArCo: the Italian Cultural Heritage Knowledge Graph, ISWC2019
[3] Experimenting with eXtreme design, EKAW2010
[4] http://www.ontologydesignpatterns.org
[5] https://essepuntato.it/lode/
[6] http://vowl.visualdataweb.org
[7] http://vowl.visualdataweb.org/webvowl.html