[Virtuoso-users] Problems running SPARQL queries through Jena

[Kjetil Kjernsmo]

All,

I've created a simple servlet to be able to get RDF/XML-ABBREV formatted 
results for parts of my application, which depends on that syntax.

It works fine for trivial DESCRIBEs (i.e. just DESCRIBE a single URI), but for 
slightly more complex queries, I get this error:

com.hp.hpl.jena.shared.JenaException: Convert results are 
FAILED.:virtuoso.jdbc3.VirtuosoException: Bad column number : 2 not in 1<n<1
        virtuoso.jena.driver.VirtuosoQueryExecution.execDescribe(Unknown Source)
        virtuoso.jena.driver.VirtuosoQueryExecution.execDescribe(Unknown Source)
        
com.computas.sublima.query.servlets.VirtJenaEndpoint.doGet(VirtJenaEndpoint.java:41)
        javax.servlet.http.HttpServlet.service(HttpServlet.java:689)
        javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
        
org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:63)
        
org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:75)
        
com.computas.sublima.app.filter.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:24)

An example of a query is this:
PREFIX dct: <http://purl.org/dc/terms/>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
PREFIX skos: <http://www.w3.org/2004/02/skos/core#>
PREFIX wdr: <http://www.w3.org/2007/05/powder#>
DESCRIBE ?resource 
<http://xmlns.computas.com/topic/topic000273> ?publisher ?subjects ?rest
WHERE {
        ?resource dct:language ?lang;
                                 dct:publisher ?publisher ;
                dct:subject 
<http://xmlns.computas.com/topic/topic000273>, ?subjects ;
        wdr:describedBy 
<http://sublima.computas.com/status/godkjent_av_administrator> ;
                ?p ?rest .}

If I run this through the Virtuoso SPARQL Endpoint, it returns the correct 
results, but crashes if I run it through Jena. The core of my servlet code is 
this:
        VirtGraph vGraph = new VirtGraph(
                SettingsService.getProperty("sublima.database.url"),
                SettingsService.getProperty("sublima.database.username"),
                SettingsService.getProperty("sublima.database.password")
        );
        Query sparql = null;
        try {
            sparql = QueryFactory.create(req.getParameterValues("query")[0]);
        } catch (QueryException e) {
            res.sendError(400, "The SPARQL query was malformed: " + 
e.getMessage());
            e.printStackTrace();
            return;
        }
        VirtuosoQueryExecution exec = 
VirtuosoQueryExecutionFactory.create(sparql, vGraph);
        Model model = exec.execDescribe();
        res.setContentType("application/rdf+xml");
        PrintWriter out = res.getWriter();
        model.write(out, "RDF/XML-ABBREV");
        out.close();

The exception message doesn't mean much to me, can anybody give more details 
about what this means?



Kind regards 

Kjetil Kjernsmo
-- 
Senior Knowledge Engineer
Mobile: +47 986 48 234
Email: kjetil.kjern...@computas.com   
Web: http://www.computas.com/

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