// get root node of coreSPARQL query...
root = SPARQL1_1Parser.parse(corequery);
// generate VisualQuery and get root element of it...
final VisualQueryGenerator vqg = new VisualQueryGenerator(
((VisualGraphOperatorWithPrefix) this.visualGraphs.get(0)).prefix);
final Operator rootNode = (Operator) root.jjtAccept(
(SPARQL1_1ParserVisitor) vqg, null);
rootNode.setParents();