Re: SHACL for SHACL

Thanks Holger

see inline

On Tue, Apr 4, 2017 at 6:27 AM, Holger Knublauch <holger@topquadrant.com>
wrote:

> Hi Dimitris,
>
>
> On 4/04/2017 5:35, Dimitris Kontokostas wrote:
>
> Another comment
>
> there are also a few recursive shapes that by definition are undefined
>
> shsh:ShapeShape a sh:NodeShape ;
>   sh:property [
>     sh:path sh:node ;
>     sh:node *shsh:NodeShapeShape* ; # node-node
>   ] ;
>   sh:property [
>     sh:path ( sh:xone [ sh:zeroOrMorePath rdf:rest ] rdf:first ) ;
>     sh:node* shsh:ShapeShape* ; # xone-members-node
>   ] ;
> sh:property [
> sh:path sh:not ;
> sh:node *shsh:ShapeShape* ;       # not-node
> ] ;
> sh:property [
> sh:path ( sh:and [ sh:zeroOrMorePath rdf:rest ] rdf:first ) ;
> sh:node *shsh:ShapeShape* ;       # and-members-node
> ] ;
> sh:property [
> sh:path sh:property ;
> sh:node *shsh:PropertyShapeShape* ;    # property-node
> ] ;
> .
>
> shsh:NodeShapeShape  a sh:NodeShape ;
>   sh:node *shsh:ShapeShape* ;
> .
>
> shsh:PropertyShapeShape  a sh:NodeShape ;
>   sh:node *shsh:ShapeShape* ;
> .
>
> shsh:PathShape
>   sh:xone (
>
> [ sh:nodeKind sh:BlankNode ;    # 2.3.1.5: Zero-or-more path
>  sh:closed true ;
>  sh:property [
>    sh:path sh:zeroOrMorePath ;
>    sh:node *shsh:PathShape* ; # multiple similar cases in the same shape
>    sh:minCount 1 ;
>    sh:maxCount 1 ;
>  ]
> ]
> [ sh:nodeKind sh:BlankNode ;    # 2.3.1.3: Alternative path
>  sh:closed true ;
>  sh:property [
>    sh:path sh:alternativePath ;
>    sh:node *shsh:PathListWithAtLeast2Members* ; # multiple similar cases
> in the same shape
>    sh:minCount 1 ;
>    sh:maxCount 1 ;
>  ]
> ]
>
> shsh:PathListWithAtLeast2Members
> a sh:NodeShape ;
> sh:node shsh:ListShape ;
> sh:property [
> sh:path ( [ sh:zeroOrMorePath rdf:rest ] rdf:first ) ;
> sh:node *shsh:PathShape* ;
> ] ;
>
>
> Ok thanks for reminding me of this. I have restructured a few shapes so
> that they avoid recursion and instead use path operations. I would
> appreciate if these change could be reviewed as it is easy to get things
> wrong at this level of complexity - e.g. writing meta-paths to traverse
> SHACL paths.
>
>     https://github.com/w3c/data-shapes/commit/
> 0c212df3674924b308223acdfdd78bba6c858eb4
>
> Note that I have avoided recursion by adding sh:targetXY statements, e.g.
> shsh:NodeShapeShape sh:targetObjectsOf sh:node. This work-arounds does work
> in our case, but I don't think this is a general design pattern that others
> can follow to avoid recursion too.
>
> Unfortunately this exercise confirms my long-held belief that the current
> work-around to avoid structural recursion leads to unmaintainable and
> redundant shape definitions. SHACL users will get negatively surprised by
> this. I believe we have made a mistake in SHACL by generally making
> structural recursion undefined. Instead we should have made runtime
> recursion undefined, i.e. the cases in which the same node is visited
> twice. We ended up with the current compromise after long long discussions,
> trying to reconcile a wide spectrum of viewpoints, including Peter's
> preference to completely disallow recursion.
>

No recursion would be neded at all and the shapes would be much simpler if
all the rdf:type statement were in the shacl graph


>
> On Mon, Apr 3, 2017 at 6:26 PM, Dimitris Kontokostas <
> kontokostas@informatik.uni-leipzig.de> wrote:
>
>> Thanks Holger,
>>
>> Although I didn´t check the actual shapes in detail I have a couple of
>> comments on some annotations
>> We have the following triple:
>>
>>> shsh: a owl:Ontology ;
>>
>>
>> Do we need shsh to be an owl ontology?
>>
>
> No, this is not needed. However several tools use the rdf:type
> owl:Ontology triple to find the graph URI if they find a local file. I see
> no costs in keeping the owl:Ontology triple.
>

There was quite a discussion for decoupling SHACL from OWL and the spec was
recently restrucuted based on that.


>
>
>
>> Do we also need to import the SHACL vocabulary?
>>
>>> shsh: owl:imports sh: ;
>>
>> I think we only need a few subclass relations which we could duplicate to
>> make it standalone
>>
>
> I think it's a good practice to owl:import the namespace that shapes are
> about. I have not tested whether this owl:import is necessary.
>

conformance to owl:imports is a SHOULD in the spec. If there is anything
needed from that file it should be copied over to the document
since triples will be copied, the statement will be also redundant


>
>
>> I am not sure if this is needed as well, we do not have SHACL-SPARQL
>> constraints
>>
>>> sh:declare [
>>> sh:prefix "shsh" ;
>>> sh:namespace "http://www.w3.org/ns/shacl-shacl#" ;
>>> ] .
>>
>>
> These are not needed either, but I believe we should try to establish and
> support a best practice in which each RDF file that defines a namespace
> also declares the prefix in a triple-ized form. This will make it easier to
> avoid clashes in the future and makes prefixes more explicit.
>

I agree on the best practices but only where it makes sense.
even if a file defines another  ns for shsh, this will have no neffect on
this file, even if both files get merged


>
> Holger
>
>
>
>
>
>> On Mon, Apr 3, 2017 at 10:45 AM, Holger Knublauch <holger@topquadrant.com
>> > wrote:
>>
>>> Thanks, good catch. Fixed.
>>>
>>> Holger
>>>
>>>
>>>
>>> On 3/04/2017 18:34, Olivier Corby wrote:
>>>
>>>> Hi,
>>>>
>>>> On 04/03/2017 04:13 AM, Holger Knublauch wrote:
>>>>
>>>>> ACTION: Everyone please review the SHACL file above, and/or try it
>>>>> against shape definitions - we should sign this off in the Wednesday
>>>>> meeting so that we can swiftly resubmit the CR request.
>>>>>
>>>>
>>>>
>>>> I think there is a problem with the URIs shsh:PropertyShape and
>>>> shsh:PropertyShapeShape, they should be the same URI :
>>>>
>>>>
>>>> sh:property [
>>>>         sh:path sh:property ;
>>>>         sh:node shsh:PropertyShape ;    # property-node
>>>>     ] ;
>>>>
>>>>
>>>>
>>>> shsh:PropertyShapeShape
>>>>     a sh:NodeShape ;
>>>>     sh:targetSubjectsOf sh:path ;
>>>>     sh:node shsh:ShapeShape ;
>>>>     sh:property [
>>>>         sh:path sh:path ;
>>>>         sh:maxCount 1 ;                 # path-maxCount
>>>>         sh:minCount 1 ;                 # PropertyShape-path-minCount
>>>>         sh:node shsh:PathShape ;        # path-node
>>>>     ] ;
>>>>
>>>>
>>>> The same problem occurs with shsh:NodeShapeShape and shsh:NodeShape
>>>>
>>>>
>>>>
>>>> Olivier
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>
>>>
>>
>>
>> --
>> 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
>>
>
>
>
> --
> 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
>
>
>


-- 
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