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Re: type and instance and subclass in SHACL documents

From: Dimitris Kontokostas <kontokostas@informatik.uni-leipzig.de>
Date: Wed, 11 May 2016 17:26:51 +0300
Message-ID: <CA+u4+a0m1vhyNpfQoskJpyuo7UAgUMnsOS+od+nRg0ku6SdEXw@mail.gmail.com>
To: "Peter F. Patel-Schneider" <pfpschneider@gmail.com>
Cc: Holger Knublauch <holger@topquadrant.com>, public-data-shapes-wg <public-data-shapes-wg@w3.org>
On Wed, May 11, 2016 at 4:30 PM, Peter F. Patel-Schneider <
pfpschneider@gmail.com> wrote:

> But SHACL does do RDFS inferencing in the data graph.  In particular, the
> sh:class depends in RDFS inferencing, namely inference rule rdfs11 from
> https://www.w3.org/TR/rdf11-mt/#rdfs-entailment.  At one time sh:class
> also
> depended on inference rules rdfs4a and rdfs4b as well as the RDFS axiom
> rdf:first rdfs:domain rdf:List .
>
> So saying that SHACL doesn't do RDFS inferencing in the data graph is
> incorrect.
>

Correct, so I will slightly revise

we say that SHACL uses rdf and rdfs terms but a shacl processors takes two
immutable graphs (shapes & data) and performs no rdfs inferencing on the
graphs at all
except for two cases: sh:classScope and sh:class
any other inferencing must be performed as a preprocessing step and is out
of scope for shacl

... define the term "shacl instance" and give more details on sh:classScope
and sh:class

The wording now is noway near perfect but if you agree with this direction
maybe you can help us write it down in a nicer way


>
>
> Simmilarly SHACL does RDFS inferencing in the shapes graph when it accepts
> ex:s1 as a shape in
>
> ex:Shape rdfs:subClassOf sh:Shape .
> ex:s1 rdf:type ex:Shape ;
>  sh:scopeClass ex:Person ;
>  sh:constraint [ rdf:type sh:NodeConstraint ;
>                  sh:nodeKind sh:IRI ] .
>
> (This appears to be an acceptable SHACL shape, based on the SHACL
> specification.)
>
>
> Of course, SHACL does not do *complete* RDFS inferencing.  In particular,
> there is no SHACL shape in
>
> ex:subClassOf rdfs:subPropertyOf rdfs:subClassOf .
> ex:Shape ex:subClassOf sh:Shape .
> ex:s1 rdf:type ex:Shape ;
>  sh:scopeClass ex:Person ;
>  sh:constraint [ rdf:type sh:NodeConstraint ;
>                  sh:nodeKind sh:IRI ] .
>

Both of these cases can be considered (imho) edge cases.
I believe no one will object to disallow them if we can get to a resolution

Dimitris


> peter
>
>
>
>
> On 05/11/2016 01:58 AM, Dimitris Kontokostas wrote:
> > I am reopening this old thread which is more related to the other open
> > discussions we have atm.
> >
> > Looking at Tom Baker's emails and in particular [1] (the first three
> > paragraphs under discussion) I was wondering if this can be a way forward
> >
> > in particular say that SHACL uses rdf and rdfs terms but a shacl
> processors
> > takes two immutable graphs (shapes & data) and performs no rdfs
> inferencing on
> > the graphs at all
> > any inferencing must be performed as a preprocessing step and is out of
> scope
> > for shacl
> > In there we define the term "shacl instance" which is used in only two
> places
> > in the spec, in sh:classScope and sh:class and no-where else
> > if people believe that we should disallow optional rdf:type statements
> (e.g.
> > for sh:property) I do not mind if this can unblock the current situation
> > Peter, would using the terms instance, class or subClassOf be fine under
> these
> > conditions?
> >
> > (I am also in favor of dropping sh:entailment btw)
> >
> > Any comments on this?
> >
> > Best,
> > Dimitris
> >
> > [1]
> https://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=ind1605&L=DC-ARCHITECTURE&P=3148
> >
> > On Tue, Mar 22, 2016 at 12:56 AM, Holger Knublauch <
> holger@topquadrant.com
> > <mailto:holger@topquadrant.com>> wrote:
> >
> >     This is becoming a long long thread about what is an entirely
> editorial
> >     matter. I don't think it deserves the urgency. I also do not agree
> that we
> >     are misusing these terms at all. I believe to make progress we could
> >
> >     a) try to find alternative terms (Peter suggested "SHACL instance"
> etc,
> >     but it could also be "is-a")
> >     b) follow the lead of what other, similar W3C specs are doing
> >     c) define the terms in the beginning and then use them as <span
> >     class="term">instance</span> so that the reader knows that we use
> that
> >     definition. That would be my preferred solution.
> >
> >     Looking at the OWL 2 spec [1] the term "instance" is used in many
> >     different contexts, without even being defined:
> >     - "Each OWL 2 ontology represented as an instance of this conceptual
> >     structure"
> >     - "if an individual /a:Peter/ is an instance of the class
> /a:Student/,
> >     and /a:Student/ is a subclass of /a:Person/, then from the OWL 2
> semantics
> >     one can derive that /a:Peter/ is also an instance of /a:Person/."
> >     - "Instances of the UML classes"
> >     - Class expressions represent sets of individuals by formally
> specifying
> >     conditions on the individuals' properties; individuals satisfying
> these
> >     conditions are said to be /instances/ of the respective class
> expressions"
> >     - ...
> >
> >     Not only does OWL use the term "instance" inconsistently but even
> changes
> >     the RDF term by applying additional OWL semantics. RDFS does not
> have the
> >     monopoly on these terms.
> >
> >     The problem is not our use of these terms but the misleading section
> 1.1
> >     that needs to be replaced. I liked a previous proposal from Dimitris,
> >     along the lines of "SHACL is based on pattern matching like SPARQL.
> >     Inferencing is not required but there is no harm if inferencing is
> >     activated (be it OWL or RDFS inferencing)". Then define the terms
> similar
> >     to what we currently have at the end of section 1.1. And that's it.
> >
> >     Holger
> >
> >
> >
> >     https://www.w3.org/TR/owl2-syntax/
> >
> >
> >     On 22/03/2016 4:15, Peter F. Patel-Schneider wrote:
> >>     I don't think that this helps at all.  In fact, all that it does is
> further
> >>     obfuscate the issue.  The issue is that the wording needs to be
> clear that in
> >>
> >>       sh:shape rdf:type my:Shape .
> >>       my:subClassOf rdfs:subPropertyOf rdfs:subClassOf.
> >>       my:Shape my:subClassOf sh:Shape .
> >>
> >>     my:Shape is not a SHACL shape, but that in
> >>
> >>       sh:shape rdf:type my:Shape .
> >>       my:Shape rdfs:subClassOf sh:Shape .
> >>
> >>     it is.
> >>
> >>     There are many cases where the SHACL notion of subclass, instance,
> typing,
> >>     etc., diverges from the common definition of these notions.
> >>
> >>     peter
> >>
> >>
> >>     On 03/21/2016 02:05 AM, Dimitris Kontokostas wrote:
> >>>     Hi Peter, I did some research on other w3c specs regarding the
> term instance.
> >>>
> >>>     if we changed occurrences of instance from e.g.
> >>>     "shapes are the instances of sh:Shape" to
> >>>     "sh:Shape is the class of all shapes"
> >>>     would this be fine from your side?
> >>>
> >>>     Some cases like sh:class and sh:classScope would need extra care
> of course.
> >>>
> >>>     On Mon, Mar 14, 2016 at 12:24 AM, Peter F. Patel-Schneider
> >>>     <pfpschneider@gmail.com <mailto:pfpschneider@gmail.com> <mailto:
> pfpschneider@gmail.com> <mailto:pfpschneider@gmail.com>> wrote:
> >>>
> >>>         Even in this situation I think that "instance" in the rest of
> the document
> >>>         needs to be qualified.  Some readers of the document will know
> about RDFS
> >>>         instance and will need to be continually reminded that the
> meaning that they
> >>>         know for "instance" is not being used in this document.
> >>>
> >>>         peter
> >>>
> >
> >
> >
> >
> > --
> > Dimitris Kontokostas
> > Department of Computer Science, University of Leipzig & DBpedia
> Association
> > Projects: http://dbpedia.org, http://rdfunit.aksw.org,
> > http://aligned-project.eu <http://aligned-project.eu/>
> > Homepage:http://aksw.org/DimitrisKontokostas
> > Research Group: AKSW/KILT http://aksw.org/Groups/KILT
> >
>
>


-- 
Dimitris Kontokostas
Department of Computer Science, University of Leipzig & DBpedia Association
Projects: http://dbpedia.org, http://rdfunit.aksw.org,
http://aligned-project.eu
Homepage: http://aksw.org/DimitrisKontokostas
Research Group: AKSW/KILT http://aksw.org/Groups/KILT
Received on Wednesday, 11 May 2016 14:30:16 UTC

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