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Re: more on recursion [was Re: fun with sh:hasShape]

From: Holger Knublauch <holger@topquadrant.com>
Date: Tue, 22 Nov 2016 15:45:33 +1000
To: public-rdf-shapes@w3.org
Message-ID: <d4847986-beed-1564-c19b-16d2edf62164@topquadrant.com>
I have extended this to explicitly enumerate the shape-expecting parameters

https://github.com/w3c/data-shapes/commit/ee37c585cc9bb1900c8d690d811b2141a3c4c7cc

Holger


On 22/11/2016 9:11, Dimitris Kontokostas wrote:
> Thank you for your feedback Peter,
>
> I updated the recursive shapes definition with your suggestions.
> https://github.com/w3c/data-shapes/commit/1583bd6db8e1b08ecf1b3f747f7245486f4288cd
>
> Best,
> Dimitris
>
> On Mon, Nov 21, 2016 at 3:58 PM, Peter F. Patel-Schneider 
> <pfpschneider@gmail.com <mailto:pfpschneider@gmail.com>> wrote:
>
>     It does appear that now the only way for the validation of one
>     shape to
>     initiate validation of another shape is via the about six constraint
>     components that take shapes as parameter values.  This means no
>     more filter
>     shapes.  It also means that there is no way that SPARQL-based
>     SHACL constructs
>     can initiate processing of another shape.  This further means that
>     the core
>     SHACL constructs provide facilities that cannot be obtained
>     through the SPARQL
>     extension.
>
>     In this considerably-changed SHACL the wording appears to be
>     getting close to
>     the intent of recursive shapes, i.e., that a recursive shape
>     points back to
>     itself via a chain of triples whose predicates are each
>     sh:property or one of
>     the shape-expecting constraint parameters.  However, I do not
>     think that the
>     wording is yet adequate.  Something along the following lines is
>     required:
>
>     "A shape *directly uses* another shape when that other shape is
>     the value of a
>     shape-expecting constraint parameter of the shape itself or one of the
>     property constraints of the shape.  The *uses* relationship
>     between shapes is
>     the transitive closure of the directly uses relationship.  A shape is
>     *recursive* if it uses itself."
>
>     The handling of recursive shapes is also problematic as it appears
>     that a
>     SHACL processor is supposed to do something useful with recursive
>     shapes.  The
>     wording should be expanded to allow SHACL processors to refuse to
>     do anything
>     with recursive shapes, i.e., by producing some sort of error
>     during syntactic
>     checking of shapes.
>
>
>     Another problem with the current wording is that it permits
>     parameters like
>     sh:minCount to contribute to recursive shape determination.
>
>     peter
>
>
>     On 11/21/2016 02:10 AM, Dimitris Kontokostas wrote:
>     > Dear Peter,
>     >
>     > Could you please check if you have further comments on the
>     definition of
>     > recursive shapes?
>     > http://w3c.github.io/data-shapes/shacl/#shapes-recursion
>     <http://w3c.github.io/data-shapes/shacl/#shapes-recursion>
>     >
>     > Best regards,
>     > Dimitris
>     >
>     > On Tue, Sep 27, 2016 at 1:51 PM, Peter F. Patel-Schneider
>     > <pfpschneider@gmail.com <mailto:pfpschneider@gmail.com>
>     <mailto:pfpschneider@gmail.com <mailto:pfpschneider@gmail.com>>>
>     wrote:
>     >
>     >     I don't think that that the new wording is adequate.
>     >
>     >     "A recursive shape is a shape thar refers to itself directly
>     or transitively
>     >     via shape-based constraint components (i.e. sh:shape),
>     logical constraint
>     >     components (i.e. sh:or), filter shapes (sh:filterShape) or
>     the sh:hasShape
>     >     SPARQL function as defined in appendix A. The handling of
>     recursive shapes is
>     >     not defined in SHACL and is left to SHACL processor
>     implementations."
>     >
>     >     s:s1 doesn't refer to itself.  Instead, the validation of
>     s:s1 on ex:foo5 ends
>     >     up having the determination of whether a violation should be
>     reported
>     >     depending on whether a violation should be reported, even
>     though there is no
>     >     path from s:s1 back to itself in the shapes graph. 
>     Different wording is
>     >     needed to describe this newly-detected problem with sh:hasShape.
>     >
>     >     The wording also continues to not distinguish between
>     >
>     >     ex:sr rdf:type sh:Shape ;
>     >       sh:class ex:c ;
>     >       sh:property [ rdf:type sh:ProperyConstraint;
>     >                     sh:predicate ex:p ; sh:shape ex:sr ] .
>     >
>     >     and
>     >
>     >     ex:sr rdf:type sh:Shape ;
>     >       ex:class ex:c ;
>     >       rdfs:seeAlso [ rdf:type sh:ProperyConstraint;
>     >                      sh:predicate ex:p ; sh:shape ex:sr ] .
>     >
>     >
>     >
>     >     There needs to be a better definition of what counts as a
>     recursive shape in
>     >     SHACL.
>     >
>     >
>     >     Peter F. Patel-Schneider
>     >     Nuance Communications
>     >
>     >
>     >
>     >
>     >     On 09/27/2016 12:44 AM, Dimitris Kontokostas wrote:
>     >     > As with other types of recursion, this is also unspecified
>     in the spec
>     >     >
>     >     > I placed the sh:hasShape function in the recursive shape list
>     >     >
>     >
>     https://github.com/w3c/data-shapes/commit/52396ff9014e055a6332c28516ac0574fb3c3211
>     <https://github.com/w3c/data-shapes/commit/52396ff9014e055a6332c28516ac0574fb3c3211>
>     >   
>      <https://github.com/w3c/data-shapes/commit/52396ff9014e055a6332c28516ac0574fb3c3211
>     <https://github.com/w3c/data-shapes/commit/52396ff9014e055a6332c28516ac0574fb3c3211>>
>     >     >
>     >     > On Mon, Sep 26, 2016 at 10:01 PM, Peter F. Patel-Schneider
>     >     > <pfpschneider@gmail.com <mailto:pfpschneider@gmail.com>
>     <mailto:pfpschneider@gmail.com <mailto:pfpschneider@gmail.com>>
>     >     <mailto:pfpschneider@gmail.com
>     <mailto:pfpschneider@gmail.com> <mailto:pfpschneider@gmail.com
>     <mailto:pfpschneider@gmail.com>>>> wrote:
>     >     >
>     >     >     What happens here?  Why?  Is what happens reasonable?
>     >     >
>     >     >
>     >     >     Data graph
>     >     >
>     >     >     @prefix rdf:
>     <http://www.w3.org/1999/02/22-rdf-syntax-ns#
>     <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
>     >     <http://www.w3.org/1999/02/22-rdf-syntax-ns#
>     <http://www.w3.org/1999/02/22-rdf-syntax-ns#>>
>     >     >     <http://www.w3.org/1999/02/22-rdf-syntax-ns#
>     <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
>     >     <http://www.w3.org/1999/02/22-rdf-syntax-ns#
>     <http://www.w3.org/1999/02/22-rdf-syntax-ns#>>>> .
>     >     >     @prefix sh:  <http://www.w3.org/ns/shacl#> .
>     >     >     @prefix ex:  <http://example.org/ex/> .
>     >     >     @prefix s:   <http://example.org/s/> .
>     >     >
>     >     >     ex:foo1 rdf:type ex:foo ;
>     >     >             rdf:type ex:bar ;
>     >     >       s:shape s:bar .
>     >     >
>     >     >     ex:foo2 rdf:type ex:foo ;
>     >     >             rdf:type ex:baz ;
>     >     >       s:shape s:bar .
>     >     >
>     >     >     ex:foo3 rdf:type ex:foo ;
>     >     >             rdf:type ex:baz ;
>     >     >       s:shape s:baz .
>     >     >
>     >     >     ex:foo4 rdf:type ex:foo ;
>     >     >             rdf:type ex:baz ;
>     >     >       s:shape s:s0 .
>     >     >
>     >     >     ex:foo5 rdf:type ex:foo ;
>     >     >             rdf:type ex:baz ;
>     >     >       s:shape s:s1 .
>     >     >
>     >     >     ex:foon1 rdf:type ex:foon ;
>     >     >             rdf:type ex:baz ;
>     >     >       s:shape s:s2 .
>     >     >
>     >     >
>     >     >
>     >     >     Shapes graph
>     >     >
>     >     >     @prefix rdf:
>     <http://www.w3.org/1999/02/22-rdf-syntax-ns#
>     <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
>     >     <http://www.w3.org/1999/02/22-rdf-syntax-ns#
>     <http://www.w3.org/1999/02/22-rdf-syntax-ns#>>
>     >     >     <http://www.w3.org/1999/02/22-rdf-syntax-ns#
>     <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
>     >     <http://www.w3.org/1999/02/22-rdf-syntax-ns#
>     <http://www.w3.org/1999/02/22-rdf-syntax-ns#>>>> .
>     >     >     @prefix sh:  <http://www.w3.org/ns/shacl#> .
>     >     >     @prefix ex:  <http://example.org/ex/> .
>     >     >     @prefix s:   <http://example.org/s/> .
>     >     >
>     >     >     s:s1 rdf:type sh:Shape ;
>     >     >       sh:targetClass ex:foo ;
>     >     >       sh:sparql [
>     >     >         sh:select
>     >     >           """SELECT $this WHERE {
>     >     >             $this s:shape ?shape ;
>     >     >             BIND (sh:hasShape($this,?shape,$shapesGraph)
>     AS ?hasShape)
>     >     >             BIND (!bound(?hasShape) AS ?failure )
>     >     >             FILTER (?failure || !?hasShape) }""" ] .
>     >     >
>     >     >     s:bar sh:class ex:bar .
>     >     >
>     >     >     s:baz sh:class ex:baz .
>     >     >
>     >     >     s:s2 rdf:type sh:Shape ;
>     >     >       sh:targetClass ex:foon ;
>     >     >       sh:sparql [
>     >     >         sh:select
>     >     >           """SELECT $this WHERE {
>     >     >             $this s:shape ?shape ;
>     >     >             BIND (sh:hasShape($this,?shape,$shapesGraph)
>     AS ?hasShape)
>     >     >             BIND (!bound(?hasShape) AS ?failure )
>     >     >             FILTER (?failure || ?hasShape) }""" ] .
>     >     >
>     >     >
>     >     >     Peter F. Patel-Schneider
>     >     >     Nuance Communications
>     >     >
>     >     >
>     >     >
>     >     >
>     >     > --
>     >     > 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
>     <http://aksw.org/DimitrisKontokostas>
>     <http://aksw.org/DimitrisKontokostas
>     <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
>     <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 Tuesday, 22 November 2016 05:46:10 UTC

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