For SELECT queries, the response format is
application/sparql-results+xml by default (even without specifying the
format parameter), and the only other format I could persuade it to
offer was JSON (with format=json).
Yes, the query supports only xml and json formats now.
For CONSTRUCT queries (the useful sort :-) ), you need
format=application/rdf+xml), which returns a lovely RDF XML document.
If you omit the format parameter, you get a 'File not found' error.
For these, you can do both XML and JSON too. What you could do is run
CONSTRUCT query, which would return JSON having three fields - subject,
predicate and object - and then make a simple script in any language
that reads that JSON and processes it to output, say, ntriple-formatted
RDF. That would be not hard.
As this is just starting the SPARQL story, it would be nice to see
suggestions about how we could format the output better... Maybe some
export options in the GUI. JSON has all the data, but some processing is
required to get CONSTRUCT produce some useful RDF serialization. At
least for now.
BTW it's open source (the GUI too) so pulls to
be the way to do it ;)