Following query, using source https://work.de-meester.org/oslo.ttl, works:
SELECT ?sfrom ?pfrom ?pto ?oto ?class ?pclass ?pclassprop ?oclassprop
WHERE {
{
?sfrom ?pfrom <https://data.vlaanderen.be/ns/persoon#GeregistreerdPersoon> .
} UNION {
<https://data.vlaanderen.be/ns/persoon#GeregistreerdPersoon> ?pto ?oto .
} UNION {
<https://data.vlaanderen.be/ns/persoon#GeregistreerdPersoon> <http://www.w3.org/2000/01/rdf-schema#subClassOf> ?class .
?pclass <http://www.w3.org/2000/01/rdf-schema#domain> ?class .
?pclass ?pclassprop ?oclassprop .
}
}
However, it doesn't when using an indirect var using following query (to replace https://data.vlaanderen.be/ns/persoon#GeregistreerdPersoon):
SELECT DISTINCT ?class
WHERE {
?class <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://www.w3.org/2002/07/owl#Class> .
}
But it does work when using following static variable:
{
"class": [
"<https://data.vlaanderen.be/ns/persoon#GeregistreerdPersoon>"
]
}