Re: AW: proposal: a reifier should reify only one "thing"

Hi Felix,

On 18/04/2024 08:03, Sasaki, Felix wrote:
>
> About
>
> „
>
> I'm more and more convincedthat a reifier _should_ not reify several 
> things
>
> „
>
> And
>
> „
>
> * it is not enforced syntactically (the following is valid RDF: :t 
> rdf:object :s1, :s2. ),
> * it is not enforced semantically (the example above does not entail 
> :s1 owl:sameAs :s2 ).
>
> “
>
> What RFC2119 language would you then use for the “_should_” in your 
> statement?
>
At this point I'm not advocating for any RFC2119 language about this 
constraint, if it has no impact on compliance as suggested above.

I could however live with something in the line of

"For a given subject, rdf:reifies SHOULD not have multiple values. Note 
however that this does not prevent a graph to contain several triples 
with the same subject, the rdf:reifies predicate, and syntactically 
distinct objects, if these objects are considered to denote the same thing."

   best

> Best,
>
>
> Felix
>
> *Von: *Pierre-Antoine Champin <pierre-antoine@w3.org>
> *Datum: *Donnerstag, 18. April 2024 um 01:18
> *An: *RDF-star WG <public-rdf-star-wg@w3.org>
> *Betreff: *proposal: a reifier should reify only one "thing"
>
> Hi all,
>
> after writing my response to Phil [1], which is a refinement of the 
> arguments I made last Friday [2], I'm more and more convinced that a 
> reifier should not reify several things, because it would lead to 
> wrong expectations ("this is similar to a named graph, right?") and 
> counter-intuitive inferences (again, see my example in [1]).
>
> That being said, I would have this constraint /only/ expressed  the 
> "intended meaning" of the rdf:reifies predicate -- in a way very 
> similar to rdf:subject, rdf:predicate and rdf:object. Reading the 
> description of these predicate in [3] strongly hints at the fact that 
> they are supposed to have only one value each ("[rdf:subject] is used 
> to state *the* subject of a statement"), but
>
> * it is not enforced syntactically (the following is valid RDF: :t 
> rdf:object :s1, :s2. ),
> * it is not enforced semantically (the example above does not entail 
> :s1 owl:sameAs :s2 ).
>
> The arguments against such an enforcement (syntactic or semantic) have 
> been largely discussed already, I won't repeat them here.
>
> Finally, I want to emphasize that, although I advocate that a reifier 
> should reify only one thing, I would like to remain very vague on what 
> kind of "thing" that is, and how many (syntactically) distinct triples 
> would actually identity that thing.
>
> For example, from the following graph
>
>     :r rdf:reifies
>         <<( dbr:Linköping dbo:populationTotal 104232 )>>.
>
> it would seem appropriate to infer (under D-entailment where 
> xsd:integer ∈ D)
>
>     :r rdf:reifies
>         <<( dbr:Linköping dbo:populationTotal 104232 )>>,
>         <<( dbr:Linköping dbo:populationTotal 00104232 )>>.
>
> (I believe that it would be the case with the semantics currently 
> proposed by Enrico).
>
> From the following graph
>
>     :r rdf:reifies
>         <<( :alice :knows :bob )>>.
>     :knows a owl:SymetricProperty.
>
> MAYBE it would be appropriate to infer
>
>     :r rdf:reifies
>         <<( :alice :knows :bob )>>,
>         <<( :bob :knows :alice )>>.
>
> From the following graph
>
>     :r rdf:reifies
>         <<( :alice :worksWith :bob )>>.
>     :worksWith rdfs:subPropertyOf :knows.
>
> MAYBE it would be appropriate to infer
>
>     :r rdf:reifies
>         <<( :alice :worksWith :bob )>>,
>         <<( :alice :knows :bob )>>.
>
> I don't have a definite answer for the two examples above, and I don't 
> think that we need to answer them urgently. I'm just pointing out that 
> we have some leeway even if we settle on "a reifier reifies only one 
> thing".
>
>   pa
>
> [1] https://www.w3.org/mid/d39fcb64-66d6-4cbe-9453-a52d1cbd5259@w3.org

> [2] https://www.w3.org/2024/04/12-rdf-star-minutes.html#x169

> [3] https://www.w3.org/TR/rdf11-schema/#h3_ch_reificationvocab

>