SPARUL query to drop most graphs, using Jena API - sparql

Question

I am trying to clear most of the graphs contained in my local Virtuoso triple store, using Apache Jena, as part of my clean up process before and after my unit tests. I think that something like this should be done. First, I retrieve the graph URIs to be deleted; then I execute a SPARUL Drop operation.
String sparqlEndpointUsername = ...;
String sparqlEndpointPassword = ...;
String sparqlQueryString = ...; // Returns the URIs of the graphs to be deleted
HttpAuthenticator authenticator = new SimpleAuthenticator(sparqlEndpointUsername,
sparqlEndpointPassword.toCharArray());
ResultSet resultSetToReturn = null;
try (QueryEngineHTTP queryEngine = new QueryEngineHTTP(sparqlEndpoint, sparqlQueryString, authenticator)) {
resultSetToReturn = queryEngine.execSelect();
resultSetToReturn = ResultSetFactory.copyResults(resultSetToReturn);
while(resultSetToReturn.hasNext()){
String graphURI = resultSetToReturn.next().getResource("?g").getURI();
UpdateRequest request = UpdateFactory.create() ;
request.add("DROP GRAPH <"+graphURI+">");
Dataset dataset = ...; // how can I create a default dataset pointing to my local virtuoso installation?
// And perform the operations.
UpdateAction.execute(request, dataset) ;
}
}
;
Questions:
As shown in this example, ARQ needs a dataset to operate on. How would I create this dataset pointing to my local Virtuoso installation for an update operation?
Is there perhaps an alternative to my approach? Would using another approach (apart from jena) be a better idea?
Please note that I am not trying to delete all graphs. I am deleting only the graphs whose names are returned through the SPARQL query defined in the beginning (3rd line).

Answer 1

Your question appears to be specific to Virtuoso, and meant to remove all RDF data, so you could use Virtuoso's built-in RDF_GLOBAL_RESET() function.
This is not a SPARQL/SPARUL query; it is usually issued through an SQL connection -- which could be JDBC, ODBC, ADO.NET, OLE DB, iSQL, etc.
That said, as you are connecting through a SPARUL-privileged connection, you should be able to use Virtuoso's (limited) SQL-in-SPARQL support, a la --
SELECT
( bif:RDF_GLOBAL_RESET() AS reset )
WHERE
{ ?s ?p ?o }
LIMIT 1
(Executing this through an unprivileged connection like the default SPARQL endpoint will result in an error like Virtuoso 37000 Error SP031: SPARQL compiler: Function bif:RDF_GLOBAL_RESET() can not be used in text of SPARQL query due to security restrictions.)
(ObDisclaimer: OpenLink Software produces Virtuoso, and employs me.)

Answer 2

You can build a single SPARQL Update request:
DROP GRAPH <g1> ;
DROP GRAPH <g2> ;
DROP GRAPH <g3> ;
... ;
because in SPARQL Update one HTTP requests can be several update operations, separated by ;.