Re: [sdw] time-prov: Drop alignment axioms that lead to deprecated property (#1428)

I've stumbled onto another syntactic reason for removal of the property chain axiom.

`owl:propertyChainAxiom` does not accept `owl:DatatypeProperty`s.  It's natural-feeling for the use case underlying this PR to "share" a literal value between some object and another linked object, by making a property chain of `owl:ObjectProperty`s ending with some `owl:DatatypeProperty`.  But, then I looked at all (5) occurrences of `owl:propertyChainAxiom` on the [OWL 2 Mapping to RDF](, which includes strict syntax matching requirements.

The last occurrence of `owl:propertyChainAxiom`, in the middle of Table 16, reads like this:

> x owl:propertyChainAxiom T(SEQ y1 ... yn) .
> { n ≥ 2,
>  OPE(yi) ≠ ε for each 1 ≤ i ≤ n, and
>  OPE(x) ≠ ε }

(I.e., each _yi_ in the chain is defined as an object property.  Notation is described in Section 3.2.1.)

There is no corresponding mapping from RDF to the functional representation that reads `x owl:propertyChainAxiom T(SEQ y1 ... yn z); ... ; DPE(z) ≠ ε.`  So, if a graph contained some property chain ending with a datatype property, the last line of Section 3 ...

> At the end of this process, the graph G _must_ be empty.

... would find that the parsing process described through Section 3 didn't exhaustively match the graph, making the graph OWL 2 FULL instead of OWL 2 DL.

I saw a hint of this restriction on chains when I was first learning OWL and PROV-O some years ago.  The [Turtle encoding of PROV-O]( includes editorial notes like this:

    # ...
    :editorialNote "It is the intent that the property chain holds: (prov:qualifiedEnd o prov:atTime) rdfs:subPropertyOf prov:endedAtTime."@en ;
    # ...

I had thought it odd that they knew their intent enough to put it into English, but didn't encode it in Turtle.  I can't guess to their reasoning back then, but I now think a reason is OWL 2 DL doesn't support a chain with a datatype property.

So, it seems this PR also incidentally removes syntax that would move an adopter of this (non-normative) resource into OWL 2 FULL.

@chris-little : Would adopting a similar informal description of the intended---but not encodable in OWL---property chain be satisfactory?  E.g., borrowing and adapting the PROV-O wording style:

> It is the intent that the property chain holds: (time:hasEnd o time:inXSDDateTime) rdfs:subPropertyOf prov:endedAtTime.  However, some translation mechanism should be used to align the timestamp value to time:inXSDDateTimeStamp.

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Received on Friday, 1 March 2024 20:35:19 UTC