from a named graph in a federated query

[Steven Blanchard]

Dear Jena users,

I would like to do a federated query (with SERVICE) but on a named 
graph and not on the default graph. How it is possible?

This query works if data are in the default graph :
query = """
PREFIX biolink: <<https://w3id.org/biolink/vocab/>>
PREFIX up: <<http://purl.uniprot.org/uniprot/>>
PREFIX reaction: <<http://sparql.microbiome.studio/reaction/>>

SELECT DISTINCT
       ?reaction
       (COUNT(DISTINCT ?soft) AS ?NSOFT)
FROM <urn:x-arq:UnionGraph>
WHERE {
   SERVICE 
<<http://jena.int.microbiomestudio.fr:8080/jena-fuseki-war-4.7.0/demo>> 
{
       ?protein biolink:provided_by ?soft .
   }
   ?protein biolink:category biolink:Protein .
   ?reaction biolink:has_catalyst ?protein .

}
GROUP BY ?reaction
"""

But i have no results if data are in a named graph:
query = """
PREFIX biolink: <<https://w3id.org/biolink/vocab/>>
PREFIX up: <<http://purl.uniprot.org/uniprot/>>
PREFIX reaction: <<http://sparql.microbiome.studio/reaction/>>

SELECT DISTINCT
       ?reaction
       (COUNT(DISTINCT ?soft) AS ?NSOFT)
FROM <urn:x-arq:UnionGraph>
WHERE {
   SERVICE 
<<http://jena.int.microbiomestudio.fr:8080/jena-fuseki-war-4.7.0/demo2?graph=http://sparql.microbiome.studio/graph/SampleName>> 
{
       ?protein biolink:provided_by ?soft .
   }
   ?protein biolink:category biolink:Protein .
   ?reaction biolink:has_catalyst ?protein .

}
GROUP BY ?reaction
"""

What is the synthax to query a named graph by SERVICE ?

Thanks in advance,

Steven