No results when running SPARQL in rdf document

Question

I am new to SPARQL queries and I am using twinkle SPARQL to run a query in an rdf document that contains:

<defaultNamespac:courses rdf:ID="Cources"> <defaultNamespac:course rdf:resource="#Course1"/> <defaultNamespac:course rdf:resource="#Course10"/> <defaultNamespac:course rdf:resource="#Course2"/> <defaultNamespac:course rdf:resource="#Course3"/> <defaultNamespac:course rdf:resource="#Course4"/> <defaultNamespac:course rdf:resource="#Course5"/> <defaultNamespac:course rdf:resource="#Course6"/> <defaultNamespac:course rdf:resource="#Course7"/> <defaultNamespac:course rdf:resource="#Course8"/> <defaultNamespac:course rdf:resource="#Course9"/> </defaultNamespac:courses> 

The request is as follows:

SELECT? x? course

WHERE {? x <file:/F:/Stuff/Muaz/GUC/Met.rdf#courses> ? course}

the problem is that the results are not returned (only x and course are displayed). What's wrong? I'm starting to get nervous, Please help me as soon as you can. Thank you very much!

PS: What data types can be returned by request? (only lines or numbers ?!)

Answer 1

Just a quick guess. Is it defaultNamespac or defaultNamespace? witn a e at the end.

If this is not an error, try running the query:

 SELECT * WHERE { ?s ?p ?o } 

If I had the following RDF file, with some defaultNamepac value:

 <rdf:RDF xmlns:contact="http://www.w3.org/2000/10/swap/pim/contact#" xmlns:defaultNamespac="http://foo.bar" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"> <defaultNamespac:courses rdf:about="file:///Users/msalvadores/kk.rdf#Cources"> <defaultNamespac:course rdf:resource="file:///Users/msalvadores/kk.rdf#Course1"/> <defaultNamespac:course rdf:resource="file:///Users/msalvadores/kk.rdf#Course10"/> <defaultNamespac:course rdf:resource="file:///Users/msalvadores/kk.rdf#Course2"/> <defaultNamespac:course rdf:resource="file:///Users/msalvadores/kk.rdf#Course3"/> <defaultNamespac:course rdf:resource="file:///Users/msalvadores/kk.rdf#Course4"/> <defaultNamespac:course rdf:resource="file:///Users/msalvadores/kk.rdf#Course5"/> <defaultNamespac:course rdf:resource="file:///Users/msalvadores/kk.rdf#Course6"/> <defaultNamespac:course rdf:resource="file:///Users/msalvadores/kk.rdf#Course7"/> <defaultNamespac:course rdf:resource="file:///Users/msalvadores/kk.rdf#Course8"/> <defaultNamespac:course rdf:resource="file:///Users/msalvadores/kk.rdf#Course9"/> </defaultNamespac:courses> </rdf:RDF> 

Then the result of the above query will be as shown in the figure:

In my case with the xmlns:defaultNamespac="http://foo.bar" namespace, if I wanted to execute your particular request, I had to use the namespace ...

 SELECT ?x ?course WHERE {?x <http://foo.bar#courses> ?course } 

My advice is to always try to set namespaces to avoid these errors.