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Re: RDF* vs RDF vs named graphs

From: Pavel Klinov <pavel@stardog.com>
Date: Fri, 4 Dec 2020 11:33:00 +0100
Message-ID: <CAJ-ZGXoLbfbO6soR68a=cGRGov8Gg6rHr95Ob_LmtT7KsU=wpA@mail.gmail.com>
To: Pierre-Antoine Champin <pierre-antoine.champin@ercim.eu>
Cc: "Peter F. Patel-Schneider" <pfpschneider@gmail.com>, public-rdf-star@w3.org
On Fri, Dec 4, 2020 at 10:38 AM Pierre-Antoine Champin <
pierre-antoine.champin@ercim.eu> wrote:

> Perer,
>
> > What should be concluded from this?  Just about the most charitable
> conclusion
> > is that RDF* is unsuitable for its claimed use.
>

> the fact that the examples do not reflect the best way to address their
> use-cases using RDF* (as it is formally defined) does not mean that such a
> way does not exist.
>
> Don't get me wrong: I am not trying to minimize the fact that such
> examples are, in a way, harmful. Clearly, they have created a lot of
> misunderstanding. One could even think that the popularity of RDF* happened
> for bad reasons, because people saw in those example something that was not
> here (in the formal definition, nor in the implementations).
>

> What makes me more optimistic is, precisely, that we have implementations,
> some of them deployed in commercial products. I'll leave the implementers
> comment on that, but I'm curious to know how their customers are using
> RDF*, and whether the unicity of embedded triples raised that many problems.
>

I have yet to see any examples of serious user confusion around use of RDF*
in Stardog. We document clearly the key decisions we made re: RDF*/SPARQL*
[1] and the confusion does not arise [2]. Most people using it in Stardog
have some familiarity with the PG data model and aligning with that helps.

What typically does cause confusion is any mention of RDF reification or
use of (singleton) named graphs for statement-level metadata. While it can
be implemented that way, as soon as those details leak to users, problems
arise. People start feeling that RDF requires some obscure/complex
mechanisms for something that PG databases support easily and naturally.
And we feel pretty strongly that *anything* that increases perceived
complexity of RDF is a bad thing.

Disclaimer: YMMV, other vendors may have a different experience. I'm not
really willing to debate who's experience is the right or most
representative, just responding to Pierre-Antoine's call for vendor
comments.

[1] https://www.stardog.com/docs/#_details
[2] this isn't to say that there're no issues, just not due to confusion
re: semantics. Typical questions we have at this time are more like people
wanting to use edge properties in SHACL to validate RDF* or in R2RML to map
tables to RDF*. But we're never going to get there if we cannot even settle
on the basic syntax, semantics, and querying.


>
> Just a small comment below on one of the examples that you quote:
>
> On 03/12/2020 00:47, Peter F. Patel-Schneider wrote:
> > I certainly agree with Thomas that examples used throughout the RDF*
> documents
> > and discussions are ill-supported by the various formal definitions
> underlying
> > RDF*.
> >
> > We see
> >
> > :bob foaf:name "Bob" .
> > <<:bob foaf:age 23>>
> >    dct:creator <http://example.com/crawlers#c1> ;
> >    dct:source <http://example.net/listing.html> .
> >
> > in http://ceur-ws.org/Vol-1912/paper12.pdf
> >
> > <<:painting :height 32.1>>
> >    :unit :cm;
> >    :measurementTechnique :laserScanning;
> >    :measuredOn "2020-02-11"^^xsd:date.
> >
> > <<:man :hasSpouse :woman>>
> >    :source :TheNationalEnquirer;
> >    :webpage <http://nationalenquirer.com/news/2020-02-12>;
> >    :retrieved "2020-02-13"^^xsd:dateTime.
> >
> > in
> https://graphdb.ontotext.com/documentation/9.2/free/devhub/rdf-sparql-star.html
> >
> > <<:Bess_Schrader :employedBy :Enterprise_Knowledge . >> :dateAdded
> "2020-05-22" .
> > <<:Bess_Schrader :employedBy :Enterprise_Knowledge . >> :addedBy
> :user_bscrader .
> >
> > in https://enterprise-knowledge.com/rdf-what-is-it-and-why-do-i-need-it/
>
> I can't help but notice that the embedded triple is repeated here,
> although the intention is clearly to put two annotations on the same arc
> -- the illustrating figure leaves no doubt about that:
>
> https://enterprise-knowledge.com/cms/assets/uploads/2020/07/rdf_7.jpeg
>
> so that person does not seem to assume that multiple embedded triples
> represent different arcs...
>

That's 100% true. Drawing any conclusion from the fact that Bess decided to
repeat the embedded triple would be a mistake. It's a single graph edge
with two properties.

Cheers,
Pavel


>
>      best
>
> >
> > <<?c a rdfs:Class>> dct:source ?src ;
> >      prov:wasDerivedFrom <<?c a owl:Class>> .
> >
> > :loisLane :believes << :superman :can :fly >>.
> >
> > in https://w3c.github.io/rdf-star/rdf-star-cg-spec.html
> >
> >
> >
> > What should be concluded from this?  Just about the most charitable
> conclusion
> > is that RDF* is unsuitable for its claimed use.
> >
> > So what is RDF* good for?  I am concerned about this.
> >
> >
> > peter
> >
> >
> >
> >
>
>
Received on Friday, 4 December 2020 10:33:27 UTC

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