Implicit default-graph-uri

[Laura Morales]

I would like to configure Fuseki such that I can use 2 datasets from 2 
different locations, as if they were a single dataset.
This is my config.ttl:


<#> a fuseki:Service ;

    fuseki:endpoint [
        fuseki:operation fuseki:query
    ] ;

    fuseki:dataset [
        a ja:RDFDataset ;

        ja:namedGraph [
            ja:graphName :graph1 ;
            ja:graph [
                a tdb2:GraphTDB ;
                tdb2:location "location-1" ;
            ]
        ] ;

        ja:namedGraph [
            ja:graphName :graph2 ;
            ja:graph [
                a tdb2:GraphTDB ;
                tdb2:location "location-2" ;
            ]
        ] ;
    ] .


There is no particular reason why I used this configuration; I mostly copied it 
from the Fuseki documentation. If it can be simplified, please suggest how.

I query Fuseki with "/service/query/?default-graph-uri=urn:x-arq:UnionGraph". I 
also know that I can use "SELECT FROM <urn:x-arq:UnionGraph>". But I would like 
to know if I can configure this behavior as the default in the main 
configuration file, such that I can avoid using "x-arq:UnionGraph" entirely.
Both datasets are TDB2 and contain triples only in the default unnamed graph 
(in other words do not contain any named graph inside).