Review Comment:
This manuscript was submitted as 'full paper' and should be reviewed along the usual dimensions for research contributions which include (1) originality, (2) significance of the results, and (3) quality of writing.
(3) quality of writing
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The paper is well written, well structured, main concepts and ideas are clearly presented.
(1) originality
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The article presents a conceptualization of the domain of narratives and its specification through an ontology, expressed in first-order logic and then implemented using semantic web standards. Narratives are of utmost importance for endowing Digital Libraries with advanced visualization and exploration tools. The related works section demonstrates that authors perfectly master the topics addressed here. They have already proposed preliminary versions of an ontology of narratives and demonstrated interesting applications in the field of Digital Libraries, in particular in the context of Europeana. But in this article they present how to express the semantics of a narrative in the form of a Web Knowledge Base, following a rigorous formal methodology, which to my knowledge does not already exist in related works.
(2) significance of the results
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In this paper, the focus is put on extensively covering the domain of narratives. To this end, the authors recall the distinction between narrations (told stories) and fabulae (actual stories) and their link by reference functions. It is explained, on the one hand, how a narration can be formalized by decomposing it into meaningful events, each event being formally represented, the connection between fragments of the narration and the formalized events being performed via reference functions. On the other hand, starting from the events of a fabula, each of them can be documented to build a narrative, using the reference functions the inverse way. In this context, the authors propose to treat the fabula of a narrative as a knowledge base composed of a set of statements giving the best available approximation of the fabula according to the narrator of the narrative. In order to build such KBs, they develop a language to express formal fabula statements.
Of course, the presence of different versions of the same story manifests different point of views, that are all important and must be kept and documented, so each narrative should be a separated KB for being able to reason on one narrative while avoiding inconsistencies with other ones. The paper is about the formalization needed for building a KB representing only one narrative, which is in itself challenging.
In particular, the core of the paper is about representing time and basic temporal relations in narratives, formally defining them and rigorously stating their behaviors. It is very common, in a narration, that only a relative relation between intervals is known, i.e. it is said that an event occurs before, after, or during another event. In the fabulae KB, the authors propose to represent the relationships between the time intervals by a network called Qualitative Temporal Knowledge, whose nodes represent the time intervals in the narrative, while arcs are labeled by sets of Allen’s relations. It is absolutely essential to be able to reason about the temporal aspects of a narrative and it is also well known that the representation of time is a tricky subject, which in my opinion the authors treat here with all the necessary rigor.
Beyond the framework of narratives for digital libraries, such a work may be reused. Rather than coding ad-hoc programs to deal with time representation, with the risk of errors, this proposal defines in a declarative way the qualitative temporal knowledge networks, and, thanks to semantic web standards, their definitions could be reused. I notice that interoperability is also well taken into account by authors, by aligning their proposal with OWL Time for general applications, and CIDOC CRM for Cultural Heritage ones. This is why I consider that this article has its rightful place in a special issue of the semantic web journal devoted to cultural heritage applications.
I would only have two demands: the first one is to provide in the paper a link for accessing the current state of the implementation of NOnt with OWL and SWRL, and the second one is to add at least one concrete example to illustrate how the implementation of this very interesting proposal is used in practice in the Mingei European project.
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