Re: Is it even possible to align RDF with LPGs via reification?

On Mon, Apr 22, 2024 at 3:44 AM Gregg Kellogg <gregg@greggkellogg.net>
wrote:

> > On Apr 21, 2024, at 1:04 PM, Luke VanderHart <lvanderhart@modern.energy>
> wrote:
> >
> > Alignment with LPGs is a stated goal for some members of this working
> > group. I am curious how they reconcile this with the fact that none of
> > the proposed changes actually permit first-class edges, only
> > reifications of first-class edges.
> >
> > The following example seems to be highly motivating:
> >
> > <<#m1 | :liz :marriedTo :richard>> [:from 1964 ; to: 1975] .
> > <<#m2 | :liz :marriedTo :richard>> [:from 1980; to: 2001] .
>
> Slight not on syntax: The statement `<<#m1 | :liz :marriedTo :richard>>
> :from 1964 ; to: 1975 .` (note no []) asserts the following triples:
>
> <#m1> rdf:reifies <<(:liz :marriedTo :richard)>> .
> <#m1> :from 1964 .
> <#m1> :to 1975 .
>
> The graph may assert elsewhere `:liz :marriedTo :richard .`, but may not.
> In the LPG case, I would expect that triple to always be asserted, but
> there are interesting use cases where you want to make a claim about a
> statement that might not be asserted in the graph, and may not be true in
> any case.
>
> If you want to both reify and assert a triple, there is the annotation
> syntax:
>
> :liz :marriedTo :richard {| <#m1> | :from 1964; :to 1975 |} .
>
> The LPG use case IIRC only makes sense with asserted triples.
>
> Reifiers, which indirectly reference the triple term, mirror LPG use cases
> when there are multiple identical edges which have separate assertions.
>
> > However, querying this graph using Sparql returns no data, because
> > neither #m1 nor #m2 are actually asserted in the graph. This is
> > probably not what someone from a LPG background would expect.
>
> #m1 and #m2 are asserted in the graph, but :liz :marriedTo :richard may
> not be asserted in the graph. A SPARQL query can be constructed that will
> return useful information.
>
> > I can assert the triple, but then the semantics become unclear:
> >
> > <<#m1 | :liz :marriedTo :richard>> [:from 1964 ; to: 1975] .
> > <<#m2 | :liz :marriedTo :richard>> [:from 1980; to: 2001] .
> > :liz :marriedTo :richard .
> >
> > Which marriage does the asserted triple represent? The one from 1964,
> > the one from 1980, or neither?
>
> This does get into other things under active discussion, such as if a
> reifier only reifies a statement (triple), or could reify an event. There
> are other ways to model this in RDF, but in LPG, it may be similar to the
> following:
>
> (liz)-[:MARRIED {from: 1964, to: 1975}]->(richard)
> (liz)-[:MARRIED {from: 1980, to: 2001}]->(richard)
>
> In this case, there are two edges from :liz to :richard with different
> annotations, mirroring the RDF-star statements, but perhaps better stated
> as
>
> :liz :marriedTo :richard {| <#m1> | :from 1964; :to 1975 |}
>                                      {| <#m2> | :from 1980; :to 2001 |} .
>

That's nice Gregg and I actually tested that syntax in
https://github.com/eyereasoner/eye/blob/master/reasoning/temp/edge.ttl
and eye --pass gives
https://github.com/eyereasoner/eye/blob/master/reasoning/temp/edge-output.ttl
which looks reasonable to me :-)

Kind regards,
Jos

The graph includes a single triple asserting `:liz :marriedTo :richard`, as
> graphs cannot include duplicated triples. The reifier is necessary to be
> able to distinguish between different sets of statements on that triple, as
> LPG allows.
>
> > Is there any mechanism in any of the current proposals to associate
> > the asserted triple (which cannot have properties in RDF) with one of
> > the reifications?
>
> That is the purpose of the reifier; in RDF, it doesn’t make sense to
> distinguish between different reifiers as a triple which is part of the
> graph is true (WRT the graph) regardless of any annotations made about that
> triple. Of course, this may be an inherently confusing example and may be
> better to model events and make assertions about those events:
>
> :m1 a :MarriageEvent; :subject :liz, :richard; :from 1965 :to 1975 .
> :m2 a :MarriageEvent; :subject :liz, :richard; :from 1980; :to 2001 .
>
> > If there is no such mechanism, are we really aligning with LPGs? Some
> > use cases might be covered on the surface, but we can't truly annotate
> > asserted edges, we can only annotate statements about edges. This is a
> > subtle but meaningful distinction and seems likely to cause confusion
> > down the road.
>
> Certainly can be confusing, but I think the LPG case can also be
> confusing. The only way to talk about edges in RDF is via reification,
> either the RDF-star version, or using the original Reification vocabulary
> (rdf:Statement, :subject, :predicate, :object).
>
> Gregg
>
> > Thank you, and my apologies if this point has already been discussed
> > and I missed it.
> >
> > - Luke VanderHart
> >
>

-- https://josd.github.io