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Re: what is inferencing?

From: Karen Coyle <kcoyle@kcoyle.net>
Date: Tue, 10 May 2016 07:34:27 -0700
To: public-data-shapes-wg@w3.org
Message-ID: <5731F173.5090405@kcoyle.net>
Jim, what I understood from the discussions on inferencing (which I 
found in various minutes from about a year ago) is that we were indeed 
referring to the RDFS/OWL function of inferring additional triples in a 
graph. The general concept, as defined by Peter, does not appear to be 
what we were talking about. So I should have been clearer about the 
context of the term in my messages, especially since so much time has 
passed.

kc

On 5/10/16 6:00 AM, Jim Amsden wrote:
> Peter,
> If by inferencing, you mean the the validation results are inferred from
> information in the associated graph, then I see your point.
>
> Is the discussion about inferencing for SHACL addressing the case where
> there is the possibility of using RDFS or OWL schema information to
> infer additional triples in the graph itself that must be included in
> the SHACL evaluations? If so, that might require any conforming
> implementation to support inferencing in order to support SHACL, and
> that may not only be limiting, but it might also be undesirable in some
> usage scenarios such as those typically handled by OSLC Resource Shapes.
> And it raises the question of which inferencing.
>
> A similar argument would apply to inferencing on the SHACL graph itself
> assuming SHACL provides an RDFS schema.
>
>
>
> Jim Amsden, Senior Technical Staff Member
> OSLC and Linked Lifecycle Data
> 919-525-6575
>
>
>
>
> From:  "Peter F. Patel-Schneider" <pfpschneider@gmail.com>
> To:  RDF Data Shapes Working Group <public-data-shapes-wg@w3.org>
> Date:  05/09/2016 09:26 PM
> Subject:    what is inferencing?
> ------------------------------------------------------------------------
>
>
>
> There has been quite a bit of discussion of inferencing and SHACL recently.
> However, there has not been much discussion on the actual relationship
> between
> SHACL and inferencing.
>
> It turns out that SHACL depends entirely on inferencing.  The definition of
> sh:nodeKind, probably the simplest construct in SHACL, says "A validation
> result must be produced for each value node that does not match the
> given node
> kind."  But this is inferencing!  True, a very degenerate form of
> inferencing
> but inferencing none the less.
>
> OK, let's rule out degenerate forms of inferencing, i.e., where all that is
> required is looking at the form of an RDF term.
>
> But then there is sh:hasValue.  Its definition says "A validation result
> must
> be produced if the sh:hasValue is not among the value nodes."  This is again
> inferencing and not so degenerate as the inferencing required for
> sh:nodeKind.
> This construct succeeds or fails depending on whether a specfic triple is
> present in an RDF graph.   This is inferencing.  True, trivial
> inferencing but
> inferencing none the less.
>
> OK, let's rule out trivial forms of inferencing , i.e., where all that is
> required is determining the presence of a single triple in an RDF graph.
>
> But then there is sh:minCount.  Its definition says "A validation result
> must
> be produced if the number of value nodes is less than the value of
> sh:minCount."  This again inferencing and not inferencing that can be
> done by
> only looking for a single RDF triple.  Here the number of triples that
> satisfy
> a particular criterion has to be determined.  This is actually quite
> sophisticated inferencing indeed.
>
> It thus seems that SHACL needs sophisticated inferencing.  Nonetheless let's
> press on and rule out even the sort of inteferencing where triples have
> to be
> retrieved from an RDF graph until a set number of matching triples are
> obtained.
>
> But then there is sh:class.  The definition of sh:class says "A validation
> result must be produced for each value node that is either a literal or a
> non-literal without a matching rdf:type. A non-literal matches a type if it
> has an rdf:type value that is the given type or one of its (transitive)
> subclasses, via rdfs:subClassOf."   So sh:class depends on the determination
> of transitive closure, again a quite sophisticated kind of inference.
>
> So what does it mean that SHACL doesn't use inferencing?  As far as I
> can see
> the only true statement about SHACL and (non-)inferencing is that everything
> in SHACL can be implemented by a simple translation from a SHACL shape to a
> SPARQL query.  (This dividing line isn't even supported by the SHACL
> document
> as the translation there is not to SPARQL but some very significantly
> extended
> SPARQL.)   And even this isn't true if recursion is added to SHACL.
>
> It certainly isn't the case that the dividing line is the need to reason by
> cases (or, equivalently, to entertain multiple models).   RDFS inferencing
> does not need reasoning by cases and SHACL does not need all of RDFS
> inferencing.
>
> If there is a dividing line, it may be that SHACL inferencing is not
> inherently serial.  However, I'm not at all sure that SHACL is indeed not
> inherently serial, even with numbers written in unary and without recursion.
>
>
> The net result is that SHACL depends on inferencing, and even quite
> sophisticated inferencing at that.
>
> peter
>
>
>
>

-- 
Karen Coyle
kcoyle@kcoyle.net http://kcoyle.net
m: 1-510-435-8234
skype: kcoylenet/+1-510-984-3600
Received on Tuesday, 10 May 2016 14:37:09 UTC

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