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Re: type and instance and subclass in SHACL documents

From: Holger Knublauch <holger@topquadrant.com>
Date: Thu, 12 May 2016 08:03:05 +1000
To: public-data-shapes-wg <public-data-shapes-wg@w3.org>
Message-ID: <41f60679-375c-52e2-1f87-55ab636e9354@topquadrant.com>
SHACL doesn't do RDFS inferencing. SHACL uses a trivial and intuitive 
form of subclassing that had been invented long before RDFS, and is 
well-established in OO systems. The fact that RDFS also reinvented a 
similar technique (and added some other inferencing rules) is 
orthogonal. RDFS does not have any rights to block these concepts or the 
terms for all future technologies.

The SHACL spec doesn't use the term inferencing except to state that it 
doesn't rely on inferencing. Even if this WG decides to use other terms 
than "instance", "type" and "subclass", the effect to the end user will 
be exactly the same. It's just a matter of clarity and politics.

Holger


On 11/05/2016 23:30, Peter F. Patel-Schneider 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.
>
>
> 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 ] .
>
>
> 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
>>
Received on Wednesday, 11 May 2016 22:03:41 UTC

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