Re: RDF-star semantics: option 3 (first DRAFT)

Since we are introducing the idea of “well-formed abstract syntax”, we should take full advantage of it.

Ora


From: Franconi Enrico <franconi@inf.unibz.it>
Date: Friday, February 16, 2024 at 1:02 PM
To: Pierre-Antoine Champin <pierre-antoine@w3.org>
Cc: RDF-star Working Group <public-rdf-star-wg@w3.org>
Subject: RE: [EXTERNAL] RDF-star semantics: option 3 (first DRAFT)
Resent-From: <public-rdf-star-wg@w3.org>
Resent-Date: Friday, February 16, 2024 at 1:01 PM


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Simple entailment matching can be done once you have done the ENCODING in rdf:nameOf, rdf:subject, … (option 2).
Indeed, this can be done also if we keep triple terms and rdf:nameOf and drop triple occurrences, but also keeping the well-formedness condition (rdf:nameOf triples are the only ones where triple terms can appear, and only in object position).
—e.



On 16 Feb 2024, at 18:48, Pierre-Antoine Champin <pierre-antoine@w3.org> wrote:
On 16/02/2024 18:37, Franconi Enrico wrote:
I am advocating (in my last email) just the opposite approach:

- disallow triple terms, e.g.:

    (triple-term (iri "ex:s") (iri "ex:p") (iri "ex:o))

- and disallow rdf:nameOf triples, e.g.:

    (triple

       (iri "ex:e")

       (iri "rdf:nameOf")

       (triple-term (iri "ex:s") (iri "ex:p") (iri "ex:o))
  )

- keep only triple occurrences terms, e.g.:

    (triple
       (triple-occurence (iri "ex:e") (iri "ex:s") (iri "ex:p") (iri "ex:o))
       (iri "ex:a”)
       (iri "ex:b”)
      )

Just like in CG, there is simple encoding (in the shape of option 2) in which simple entailment based on matching works.

Even if we disallow triple terms and keep only term occurrences, the entailment between the first 2 graphs in my email holds, despite the fact there is no subgraph of one that is an instance of the other -- i.e. no pattern matching between them.

Besides simple entailment, this means that SPARQL results will be tricky to define. What should

    SELECT ?x { ?x :a :b }

return for this graph ?
x = (triple-occurrence (iri "ex:e") (iri "ex:s") (iri "ex:p") (iri "ex:o")) -- as suggested by the 1st graph?
Or x = (iri "ex:e"), as suggested by the 2nd graph?
Or both??
—e.



On 16 Feb 2024, at 18:17, Pierre-Antoine Champin <pierre-antoine@w3.org><mailto:pierre-antoine@w3.org> wrote:


Thanks Enrico for this proposal.

I strongly suggest that we get rid of the orange part, with an argument similiar to what Andy brought up during the Semantics TF call today -- and pushing Andy's argument forward.

The orange part make "triple occurrences"  part of the abstract syntax. Regardless of the name, I think it is a bad idea.

In the following, I'll use a lisp-like representation of the abstract syntax, hopefully self-explanatory.

(graph
  (triple
    (triple-occurence (iri "ex:e") (iri "ex:s") (iri "ex:p") (iri "ex:o))
    (iri "ex:a")
    (iri "ex:b")
  )
  (triple
    (iri "ex:e")
    (iri "ex:c")
    (iri "ex:d")
  )
)

According to your semantics, it would be semantically equivalent to the following graph

(graph
  (triple
    (iri "ex:e")
    (iri "ex:a")
    (iri "ex:b")
  )
  (triple
    (triple-occurence (iri "ex:e") (iri "ex:s") (iri "ex:p") (iri "ex:o))
    (iri "ex:c")
    (iri "ex:d")
  )
)

which would also be equivalent to

(graph
  (triple
    (iri "ex:e")
    (iri "ex:a")
    (iri "ex:b")
  )
  (triple
    (iri "ex:e")
    (iri "ex:c")
    (iri "ex:d")
  )
  (triple
    (iri "ex:e")
    (iri "rdf:nameOf")
    (triple-term (iri "ex:e") (iri "ex:s") (iri "ex:p") (iri "ex:o))
  )
)

We are talking about simple entailment here, not some sophisticated semantic extension.
This breaks a very important feature of the simple entailment in RDF 1.1, namely: it can be computed by doing simple pattern matching of graphs: https://www.w3.org/TR/rdf11-semantics/#dfn-interpolation


Clearly, there is no simple pattern matching method that can detect that the 3 graphs above entail each other.

  pa

On 16/02/2024 15:58, Franconi Enrico wrote:
RDF‐star semantics: option 3<https://github.com/w3c/rdf-star-wg/wiki/RDF%E2%80%90star-semantics:-option-3>
github.com<https://github.com/w3c/rdf-star-wg/wiki/RDF%E2%80%90star-semantics:-option-3>

<apple-touch-icon-180x180-a80b8e11abe2.png><https://github.com/w3c/rdf-star-wg/wiki/RDF%E2%80%90star-semantics:-option-3>



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