Find facets by SPARQL patterns

I need to be able to call PropertyPairsFacet for each node which appears in a predicate position. The facet will render all subject-object pairs for this property as a table.

Decision: Use SPARQL SHACL SHACL-SPARQL

$id: python://iolanta.facets.PropertyPairsFacet
iolanta:outputs: datatypes:textual
iolanta:pattern: ASK { ?subject $this ?object }

Consequences

Pro

• Simple and clear implementation
• No dependency on SHACL processing overhead

Contra

• Patterns are not Linked Data
  • And therefore cannot be easily reused and extended
  • But this can be amended later by support for a RDF based SPARQL serialization

Not supported by SHACL Core:

SHACL Core includes the following kinds of targets: node targets, class-based targets (including implicit class-based targets), subjects-of targets, and objects-of targets.

There are no predicates-as targets, as we can see.

Courtesy of ChatGPT

$id: https://example.com/shapes/PredicateNodeShape
$type: sh:NodeShape
sh:sparql:
  $type: sh:SPARQLConstraint
  sh:message: "Node must appear in predicate position."
  sh:ask: |-
    ASK {
      ?subject $this ?object .
    }

If we have to use SPARQL anyway then I do not see the need to employ SHACL as an intermediate layer wrapping it.