Review Comment:
The paper addresses two relevant problems in the context of CIDOC knowledge base. The first is a classical philosophical problem: the existential implications in any statement about a non existent entity. Given the language adopted by CIDOC, statements about lack of something, like a feature or a component, cause to include (implicitly or explicitly) an instance in the domain of quantification of the very entities which are declared not to exist. The second problem is of practical origin: when many instances of a feature are present it may be practically impossible to report all of them. In this case the KB may report only the existence of such type of entities without giving specifications about each.
The source of the problem is identified in the limitation of CIDOC to relationships that have as domain and as range particulars (individuals).
The proposed solution, which is original to my knowledge and marks an improvement wrt the discussed problems even though there are limitations (see below), is to introduce a new set of relations that have domain as before and range not a class of particulars but their type. In short, every statement “x has component y” turns into “x has some component of type Y” (with Y the type of the entity y).
This does not avoid contradictions due to limitations of what one may be able to observe, e.g., I guess bumps in the spine could mark the presence of sewing support for some and be only aesthetic features for others. Furthermore, badly characterized concepts still cause the presence of contradictions (is a sewing support necessarily a functional entity? How well should the function be performed? Is it enough that it was intentionally introduced for this reason even though it fails to perform?)
While the paper is generally well written and clear, some parts need to be revised. For instance, the introduction of the following problem (pg.5) is misleading since it is unaffected by the proposed approach and may confuse the reader about the purpose of the paper:
“book does not have gold-tooled decoration” (E89 Propositional Object) → P129 is about → book (E18 Physical Thing)
The problem raised by this E89 entity has different characteristics than those addressed in the paper.
The set of inferences that the new relations allow need to be extended to the broadening/narrowing of the domain entity, not only of the target type. For instance
From
book cover (E18 Physical Thing) → NTP46 is not composed of physical thing of type (is not type of physical thing which forms part of) → tooled decoration
One cannot infer
book (E18 Physical Thing) → NTP46 is not composed of physical thing of type (is not type of physical thing which forms part of) → tooled decoration
Sect. 3 introduces the proposal stating “Step 1 involves changing the range of each property to ‘E55 Type’.” This is likely badly expressed as the intent, I surmise, is to enrich CIDOC by adding the new TP and NTP properties while keeping (i.e., not substituting) the existing properties.
Finally, since the effects of this approach to discover inconsistencies depend on the possibility to reason on types and since type instances are obtained by connecting to external resources (this implies that description, quality, coverage, organization of types is not controlled by CIDOC), CIDOC may claim that the technique solved the problem while not being able to take advantage from it.
Sect. 3.2 implies that it is possible to characterize when completeness is reached and that this is stored in CIDOC but nothing is said about how this should be done.
Minor points:
“Documenting this correspondence is called ‘instantiation’ (pg.3)”
Instantiation is not about documenting relationships btw a particular and a universal, it is the ontological relationship holding btw them because one satisfies the essential conditions imposed by the other (and is independent of possible documentations).
In sect. 1.2 the sentence “Within the discourse around the CIDOC CRM there has been no previous systematic attempt to address the problem of non-existent instances.” is stated in the context of the second problem but refers to the first.
In sect. 1.3 use “i)” and “ii)” instead of “a)” and “b)” to avoid confusion with the addressed individuals a and b.
pg.4: “Note however, that the counterfactual instance may need to be instantiated in its class in order to test whether it conforms with the applicable constraints, but this instantiation is a technical fact that occurs during the execution of an algorithm on the knowledge base and does not imply existence in the underlying reality”
This is not a valid argument since the instantiation is a logical consequence of the semantics of the expression, the problem is conceptual and one should not blame the algorithm.
pg.5: E55 is confusing unless one is already familiar with CIDOC, anticipate the class with an example
pg.6: the statement “Following the realization that it is more practical to describe a) non-existent things” is weird since you just discussed all the practical problems introduced in the DB from the explicit use of non-existent things.
While the paper is detailed in presenting CIDOC’s notions, it is too verbose on concepts which are common knowledge in this community like the open/close world distinction or the discussion on inferences in Sect. 3.1.3.
pg. 8: “The CIDOC CRM observes [adopts?] the Open World assumption”
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