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Re: Simplification of scopes section (see also ISSUE-148)

From: Irene Polikoff <irene@topquadrant.com>
Date: Sat, 14 May 2016 13:05:29 -0400
Message-Id: <B0430FDD-CD55-47B7-BE18-76397AEA6D55@topquadrant.com>
Cc: Dimitris Kontokostas <kontokostas@informatik.uni-leipzig.de>, public-data-shapes-wg <public-data-shapes-wg@w3.org>
To: kcoyle@kcoyle.net
To me, this sounds like a question about what it means for a shape not to have a scope.

One answer could be - such a shape is ignored. A shape is not evaluated against any nodes unless there is a scope. 

Another answer could be - it is then becomes applicable everywhere, meaning that any node in the data graph becomes a focus node for such a shape. 

What is the current approach?

Sent from my iPhone

> On May 14, 2016, at 11:53 AM, Karen Coyle <kcoyle@kcoyle.net> wrote:
> 
> Another way to look at this is that there is a data graph that is to be addressed. If the data graph as a whole is not to be the target of the constraints, then one must apply a scope to define the subset of the graph that is the focus of the constraints. There is no change (AFAIK) in the function of the constraint between:
> 
> 
> ex:MyShape
>    a sh:Shape ;
>    rdfs:comment "every dct:subject must have IRIs as objects" ;
>    sh:scopeClass ex:Class;
>    sh:property [
>        sh:predicate dct:subject ;
>        sh:nodeKind sh:IRI ;
>    ] .
> 
> and
> 
> ex:MyShape
>    a sh:Shape ;
>    rdfs:comment "every dct:subject must have IRIs as objects" ;
>    sh:property [
>        sh:predicate dct:subject ;
>        sh:nodeKind sh:IRI ;
>    ] .
> 
> In both cases, the constraint applies to the scope of the shape; this can be either the entire data graph or a subset of the data graph. If the property constraint can function on a graph selected with rdf:type then it can function on the data graph as a whole. The pre-selection of every triple with property dct:subject seems unnecessary. It also seems hard to grasp because node and class scopes pinpoint a starting node for a graph while the property scope is going to return individual triples. These do not seem to be the same logical function.
> 
> kc
> 
> 
> 
>> On 5/14/16 5:07 AM, Dimitris Kontokostas wrote:
>> Karen's example could be modeled with multiple shapes and property
>> scopes or a single shape with allSubjectsScope and multiple sh:property
>> definitions for dct:title & dct:subject which is more efficient
>> 
>> Another gap that sh:AllSubjectsScope came to fill is sh:scopeClass
>> rdfs:Resource that was available in very early versions of SHACL
>> In general this scope gives shacl core the flexibility to define complex
>> focus nodes using all subjects + filters that will not be easy otherwise
>> so I would be keen on keeping this in core
>> 
>> On Sat, May 14, 2016 at 7:22 AM, Karen Coyle <kcoyle@kcoyle.net
>> <mailto:kcoyle@kcoyle.net>> wrote:
>> 
>>    Looking at this:
>> 
>>    On 5/13/16 5:23 PM, Holger Knublauch wrote:
>> 
>>        ex:MyShape
>>              a sh:Shape ;
>>              rdfs:comment "every dct:subject must have IRIs as objects" ;
>>              sh:scopeProperty dct:subject ;
>>              sh:property [
>>                  sh:predicate dct:subject ;
>>                  sh:nodeKind sh:IRI ;
>>              ] .
>> 
>> 
>>    There is 100% redundancy between sh:scopeProperty and the
>>    constraint. If I were to state what I want to do in terms of
>>    validation, it would come out like this:
>> 
>> 
>>    ex:MyShape
>>         a sh:Shape ;
>>         rdfs:comment "every dct:subject must have IRIs as objects" ;
>>         sh:property [
>>             sh:predicate dct:subject ;
>>             sh:nodeKind sh:IRI ;
>>         ] .
>> 
>>    because I am not using a scope at all. What this means is what is in
>>    the comment. A scope, logically, is a selection from the data graph,
>>    but this use case makes no such selection, and the constraint is
>>    sufficient.
>> 
>>    Is there a use of scopeProperty that would not be redundant?
>> 
>> 
>>    kc
>> 
>>    --
>>    Karen Coyle
>>    kcoyle@kcoyle.net <mailto:kcoyle@kcoyle.net> http://kcoyle.net
>>    m: 1-510-435-8234
>>    skype: kcoylenet/+1-510-984-3600 <tel:%2B1-510-984-3600>
>> 
>> 
>> 
>> 
>> --
>> 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
> 
> -- 
> Karen Coyle
> kcoyle@kcoyle.net http://kcoyle.net
> m: 1-510-435-8234
> skype: kcoylenet/+1-510-984-3600
> 
Received on Saturday, 14 May 2016 17:06:00 UTC

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