[redland-dev] Trouble with UNION query: RedlandWarning: Triple with unbound subject skipped

[Josh Mandel]

I've been seeing what seems like unexpected behavior when I run a
SPARQL query involving a UNION:  I get only one clause's worth of
results, and then a:

  /usr/lib/python2.6/dist-packages/RDF.py:1373: RedlandWarning: Triple
with unbound subject skipped

I'm running Python 2.6.5 and the python-librdf package distributed
with Ubuntu 10.04. Here's a snippet of code to reproduce the
problem...

What does this mean?  Is my query flawed? Any advice would be much appreciated!

  -Josh

---

import RDF

breaks = """<?xml version="1.0" encoding="utf-8"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
xmlns:test="http://test/">
   <rdf:Description>
      <rdf:type rdf:resource="http://test/a"/>
      <test:property>happy</test:property>
      <test:property>thoughts</test:property>
   </rdf:Description>

   <rdf:Description>
      <rdf:type rdf:resource="http://test/b"/>
      <test:property>sadmess</test:property>
   </rdf:Description>

</rdf:RDF>"""

model = RDF.Model()
parser = RDF.Parser()
parser.parse_string_into_model(model, breaks, "base")

model_size = len(model)

q1 = RDF.SPARQLQuery("""
    PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
    CONSTRUCT {?s ?p ?o.}
    WHERE
    {
	 {
           ?s rdf:type <http://test/a>.
           ?s ?p ?o.
         }
    UNION
         {
           ?s rdf:type <http://test/b>.
           ?s ?p ?o.
         }
    }
""")


r1 = q1.execute(model)
s1 = r1.as_stream()
c1 = 0

for v in s1:
  c1 += 1
  print v, c1

assert(c1 == model_size), "Query did not find all rows."