mixing FROM and FROM NAMED with unionDefaultGraph=true

[Simon Helsen]

Hi guys,

I have a question which may or may not be a defect, but I need some input 
first.

If you run with unionDefaultGraph==true and you have the following type of 
query:

SELECT ?o
  FROM <graphUri1>
  FROM NAMED <graphUri2> 
WHERE {  ?s <somePredicate> ?o }

I would expect the pattern to match triples in both graphUri1 and 
graphUri2. Currently, TDB/ARQ does not do this, but only picks matches 
from graphUri1. Given that unionDefaultGraph=true should merge all named 
graphs into the default graph, this is surprising. To elaborate a bit, we 
found that the following query

SELECT ?o
FROM NAMED <graphUri2> 
WHERE {  ?s <somePredicate> ?o }

does pick results from graphUri2 (when run with unionDefaultGraph==true). 
Also, when we execute the following query:

SELECT ?o
  FROM <graphUri1>
  FROM NAMED <graphUri2> 
WHERE {  graph ?g { ?s <somePredicate> ?o } }

then tdb seems to pick results from graphUri2 which is as expected.

We were thinking that explicit FROM/FROM NAMED clauses simply ignores the 
unionDefaultGraph=true switch which could then explain the behavior of the 
first query above, but it doesn't explain the one of the second query. 

Feedback on this is welcome.

thanks,

Simon