Re: sh:uniqueLang and empty lang tags

Hi,

to express the SKOS S14 constraint, we are using qualified value 
restrictions:

skos:Concept-prefLabel
   rdf:type sh:PropertyShape ;
   sh:path skos:prefLabel ;
   dash:singleLine true ;
   sh:description "The preferred lexical label for a resource, in a 
given language."@en ;
   sh:disjoint skos:altLabel ;
   sh:disjoint skos:hiddenLabel ;
   sh:group skos:LabelsAndDescriptionPropertyGroup ;
   sh:or (
       [
         sh:datatype xsd:string ;
       ]
       [
         sh:datatype rdf:langString ;
       ]
     ) ;
   sh:order 0 ;
   sh:qualifiedMaxCount 1 ;
   sh:qualifiedValueShape [
       rdfs:label "datatype string (without language tag)" ;
       sh:datatype xsd:string ;
     ] ;
   sh:uniqueLang true ;
.

When we designed the SHACL Core constraint components, we were 
attempting to provide basic building blocks that can then be combined. 
The mailing list archive may contain background minutes on this exact 
discussion related to sh:uniqueLang.

Holger


On 24/03/2020 18:56, Vladimir Alexiev wrote:
> https://www.w3.org/TR/shacl/#UniqueLangConstraintComponent says
> "for each *non-empty language tag *that is used by at least two value 
> nodes..."
>
> Why is that? I think that either of these nodes should cause a 
> validation error:
>
> :Person1 rdfs:label "Alice",    "Bob".
> :Person2 rdfs:label "Alice"@en, "Bob"@en.
>
> https://www.w3.org/TR/skos-reference/#S14 does not exclude empty tags 
> from validation, yet all examples it gives are of non-empty tags.
> Yet the intent is clear: to be able to pick a single label based on 
> some lang preferences.
> In the case of two plain strings, you can't pick one of them reliably.
>
> Cheers!
> -- 
> Vladimir Alexiev, PhD, PMP
> Chief Data Architect
> Sirma AI, trading as Ontotext: https://www.ontotext.com 
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