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Re: the current situation with respect to ISSUE-134

From: Holger Knublauch <holger@topquadrant.com>
Date: Fri, 8 Apr 2016 10:53:26 +1000
To: public-data-shapes-wg@w3.org
Message-ID: <57070106.5000409@topquadrant.com>


On 8/04/2016 0:08, Peter F. Patel-Schneider wrote:
> Here is my understanding of the intent of the current situation.  I don't
> believe that all of these are supported by explicit wording in the current
> document.
>
> 1/ OK.  The constraint has an explicit rdf:type link to
> sh:PropertyConstraint providing the valid type.
>
> @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
> @prefix sh: <http://www.w3.org/ns/shacl#> .
> @prefix ex: <http://ex.com/> .
>
> ex:s1 a sh:Shape ;
>   sh:property [ rdf:type sh:PropertyConstraint ;
>   	       sh:predicate ex:p ;
> 	       sh:nodeKind sh:IRI ] .
>
> 2/ OK. There is no rdf:type link for the constraint so default value type
> processing comes into play which provides the valid type.
>
> @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
> @prefix sh: <http://www.w3.org/ns/shacl#> .
> @prefix ex: <http://ex.com/> .
>
> ex:s1 a sh:Shape ;
>   sh:property [
>   	       sh:predicate ex:p ;
> 	       sh:nodeKind sh:IRI ] .
>
> 3/ Not OK.  The explicit rdf:type link prevents default value type
> processing from having an effect so there is no valid type.
>
> @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
> @prefix sh: <http://www.w3.org/ns/shacl#> .
> @prefix ex: <http://ex.com/> .
>
> ex:s1 a sh:Shape ;
>   sh:property [ rdf:type ex:PropertyConstraint ;
>   	       sh:predicate ex:p ;
> 	       sh:nodeKind sh:IRI ] .
>
> 4/ Not OK.  Even though the class here is the universal class the explicit
> rdf:type link prevents default value type processing from having an effect
> so there is no valid type.
>
> @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
> @prefix sh: <http://www.w3.org/ns/shacl#> .
> @prefix ex: <http://ex.com/> .
>
> ex:s1 a sh:Shape ;
>   sh:property [ rdf:type rdfs:Resource ;
>   	       sh:predicate ex:p ;
> 	       sh:nodeKind sh:IRI ] .
>
> 5/ Not OK.  There is no valid type even though the constraint is a SHACL
> instance of sh:PropertyConstraint.
>
> @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
> @prefix sh: <http://www.w3.org/ns/shacl#> .
> @prefix ex: <http://ex.com/> .
>
> ex:PropertyConstraint rdfs:subClassOf sh:PropertyConstraint .
>
> ex:s1 a sh:Shape ;
>   sh:property [ rdf:type ex:PropertyConstraint ;
>   	       sh:predicate ex:p ;
> 	       sh:nodeKind sh:IRI ] .
>
> 6/ OK.  There is an explicit rdf:type link to sh:PropertyConstraint so the
> constraint has a valid type
>
> @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
> @prefix sh: <http://www.w3.org/ns/shacl#> .
> @prefix ex: <http://ex.com/> .
>
> ex:s1 a sh:Shape ;
>   sh:Property [ rdf:type sh:PropertyConstraint ;
>   	       rdf:type ex:InversePropertyConstraint ;
>   	       sh:predicate ex:p ;
> 	       sh:nodeKind sh:IRI ] .

So far so good. (except sh:property is not uppercase).

>
> 7/ Unknown.  There is an explicit rdf:type link to sh:PropertyConstraint so
> the constraint has a valid type.  However, the constraint is a SHACL
> instance of both sh:PropertyConstraint and sh:InversePropertyConstraint.
>
> @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
> @prefix sh: <http://www.w3.org/ns/shacl#> .
> @prefix ex: <http://ex.com/> .
>
> ex:InversePropertyConstraint rdfs:subClassOf sh:InversePropertyConstraint .
>
> ex:s1 a sh:Shape ;
>   sh:Property [ rdf:type sh:PropertyConstraint ;
>   	       rdf:type ex:InversePropertyConstraint ;
>   	       sh:predicate ex:p ;
> 	       sh:nodeKind sh:IRI ] .

This is a valid example. The current spec states that
- the classes only count as disjoint if they have rdf:type triples (i.e. 
subtype inference is not applied)
- one of the values of rdf:type is sh:PropertyConstraint, so that will 
be used.

>
> 8/ Unknown.  There is an explicit rdf:type link to sh:PropertyConstraint so
> the constraint has a valid type.  However, the constraint is an
> instance of both sh:PropertyConstraint and sh:InversePropertyConstraint.
>
> @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
> @prefix sh: <http://www.w3.org/ns/shacl#> .
> @prefix ex: <http://ex.com/> .
>
> ex:subClassOf rdfs:subPropertyOf rdfs:subClassOf .
> ex:InversePropertyConstraint ex:subClassOf sh:InversePropertyConstraint .
>
> ex:s1 a sh:Shape ;
>   sh:Property [ rdf:type sh:PropertyConstraint ;
>   	       rdf:type ex:InversePropertyConstraint ;
>   	       sh:predicate ex:p ;
> 	       sh:nodeKind sh:IRI ] .

This is valid as 7 is, and rdfs:subPropertyOf rdfs:subClassOf is ignored 
(because we don't claim RDFS inferencing will be used).

>
>
> The situation with sh:constraint is even more murky, as its name seems to
> indicate that its natural range should be sh:Constraint but instead it is
> sh:NodeConstraint.

sh:constraint will also be the place for extensions, e.g. 
sh:SPARQLConstraint. Furthermore, it should be legal to use it for 
sh:PropertyConstraints - the meaning being similar to sh:property but 
with a different intent: sh:property declares a "relevant" property for 
that shape, while sh:constraint would merely add a constraint in case 
that property happens to be used (but it's not a relevant or recommended 
property).

Overall, if you have specific suggestions on what is missing, please 
send instructions on what needs to be edited.

Holger
Received on Friday, 8 April 2016 00:54:00 UTC

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