Review Comment:
The paper presents a web-based tool for visualizing and manipulating ontology alignments. The main idea on which the tool is based is that providing the user with several visualization methods and allowing simultaneous visualization of multiple alignments may facilitate the ontology alignment evaluation process. Thus, it offers visualization modes, such as trees and graphs, and the user can create several visualization profiles and switch between them depending on his needs. The tool is evaluated qualitatively by a limited number of users that were asked to answer a questionnaire regarding their experience using the tool.
The presented tool is a well-informed attempt to make a contribution to the ontology alignment visualization problem; it achieves that by supporting the several visualization modes and profiles. However, the paper focuses on describing the visualization modes, and discusses only very briefly other crucial functions that are available to support alignment visualization and editing. The paper mentions e.g. that trimming, filtering, etc. operations are available, but since it does not provide a more thorough presentation, the level of their support is unclear. In this respect, Section 4.4. should be extended to discuss in greater detail what exact type of operations are provided (i.e. what search, filtering, grouping, etc. options are available; how a "criterion" may be defined) and whether such operations are available in all visualization modes apart from the correspondences list and can be dynamically applied on any of them. Moreover, with respect to multiple visualization modes, although it is useful to provide two visualizations side-by-side, one could imagine a more dynamic interface where e.g. additional visualizations (more than two) might be added or removed as needed.
Apart from the above, as recognized by the authors themselves, the main drawback of the tool is that its usefulness is limited to rather small ontologies. The paper should state whether this is a scalability problem due to the fact the system cannot handle the computational load of the visualization of a very large number of alignments, or because the practical value of a complete graphical visualization of alignments is reduced when ontologies are very large. In this respect the authors could consider combining dynamic filtering, grouping, etc. operations discussed above as well as other approaches when visualizing alignments for large ontologies.
Finally, the practical use of the tool would be further supported if the authors provided some real use cases and challenges (apart from introductory courses on ontologies) where the tool was successfully used in practice.
Some other comments:
p.3 c.2 l.4-11: It should be defined what are simple/single, and complex/multiple alignments, so that e.g. the two sentences "However, they (i.e. [2,8,25]) are limited to visualization of **single** alignments and offer limited support ...", and "Differently from [4], VOAR is limited to the visualization of **simple** alignments" are clear and do not contradict each other.
p.5 c.1 l.7: "offer" -> offers
p.5 c.2 l.9-11: "Similar to the... 6)". sentence in bad English, please rephrase
p.5 c.2 l.23: "has an inefficient use of screen space displayed" -> phrase in bad English, please rephrase
p.6 c.1 last sentence: "Allowing ... preferences." the sentence seems to be incomplete, please check
p.7 c.2 l.6: "rigth" -> right
p.8 c.2 l.-10: "as" -> is
p.9 c.1 l.-3: "positives" -> positive
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