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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 11:58:22 +0300
Message-ID: <CA+u4+a2bmsXCxBL_qWAxjjYzUpwfDq3=2d7Y+bn=M9HpWeLQ+A@mail.gmail.com>
To: Holger Knublauch <holger@topquadrant.com>
Cc: public-data-shapes-wg <public-data-shapes-wg@w3.org>
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
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?



On Tue, Mar 22, 2016 at 12:56 AM, Holger Knublauch <holger@topquadrant.com>

> 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> <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,
Research Group: AKSW/KILT http://aksw.org/Groups/KILT
Received on Wednesday, 11 May 2016 09:01:41 UTC

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