Re: labelled property graphs vs -star extension of RDFn vs -star extension of named graphs

Assuming:

    PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
    PREFIX : <http://example.org/ns/>
    BASE <http://example.org/>

With RDF-star source:

    <liz> :spouse <dick> {| :start 1964; :end 1974 |} .
    <liz> :spouse <dick> {| :start 1975; :end 1976 |} .

And RDF-star query:

    ASK { :liz :spouse :dick {| :start 1964; :end 1976 |} . }

From the token-based alternatives I'm exploring (see e.g. [1]), we
have two options based on existing RDF.


1. If short for RDF named graphs (and ignoring needed semantics for datasets):

    <liz> :spouse <dick> .

    _:g1 { <liz> :spouse <dick> }
    _:g1 :start 1964 ;
      :end 1974 .

    _:g2 { <liz> :spouse <dick> }
    _:g2 :start 1975 ;
      :end 1976 .

The unstarred query would become (assuming no union default graph and
no need to consider opacity):

    ASK {
      <liz> :spouse <dick> .
      GRAPH ?x { <liz> :spouse <dick> }
      ?x :start 1964; :end 1976 .
    }

Result: false


2. If short for reification:

    <liz> :spouse <dick> .

    _:t1 rdf:subject <liz> ;
      rdf:predicate :spouse ;
      rdf:object <dick> ;
      :start 1964 ;
      :end 1974 .

    _:t2 rdf:subject <liz> ;
      rdf:predicate :spouse ;
      rdf:object <dick> ;
      :start 1975 ;
      :end 1976 .

The unstarred query would become:

    ASK {
      <liz> :spouse <dick> .
      ?x rdf:subject <liz> ;
        rdf:predicate :spouse ;
        rdf:object <dick> ;
        :start 1964 ;
        :end 1976 .
    }

Result: false


Best regards,
Niklas

[1]: <https://lists.w3.org/Archives/Public/public-rdf-star-wg/2023Nov/0061.html>

On Fri, Dec 8, 2023 at 3:18 PM Peter F. Patel-Schneider
<pfpschneider@gmail.com> wrote:
>
> At the teleconference yesterday I mentioned that there could be user-visible
> differences between different views of how to proceed, even when there is some
> consensus that different views are essentially the same.
>
> Here is one example of a user-visible divergence.  Consider the following
> input, written in the community group syntax.
>
> :liz :spouse :dick {| :start 1964; :end 1974 |} .
> :liz :spouse :dick {| :start 1975; :end 1976 |} .
>
> In the community graph version of RDF-star this results in one asserted triple
> with subject :liz that is the subject of four triples.  In SPARQL-star, the BGP
>
> :liz :spouse :dick {| :start 1964; :end 1976 |} .
>
> would match against a graph constructed from this input.
>
> In labelled property graphs this would appear to result in two asserted
> triples with subject :liz, each with two property-value pairs.  The above BGP
> would not match.
>
> So there is a decided visible difference between the community graph version
> of RDF-star and labelled property graphs.
>
> If I am correct in reading the (sparse) information available about RDFn, a
> -star extension of RDFn would conform to the community group reading.  So
> there would be noticeable differences between an extended RDFn and labelled
> property graphs.
>
> I am not aware of any proposal for using named graphs that says what the above
> would result in there, so it is unclear which side a named graphs version of
> -star would fit into.
>
> peter
>

Received on Friday, 8 December 2023 17:19:53 UTC