Do you mean root node or nodes? Surely there can only be one root? Or do you mean you are looking for the leafs? Mark On 18 Jun 2014, at 13:31, Borris <borris(a)chaos.org.uk&gt; wrote:

I guess it's probably useful for me to add that there are multiple such graphs and key part of the operation is which graph a datum belongs to. -- View this message in context: http://drools.46999.n3.nabble.com/Noob-question-graph-searching-query-roo... Sent from the Drools: User forum mailing list archive at Nabble.com.

It looks like your graph is not in the WM, so you can just iterate the references. Here is an example of how to do this. @Test public void testGraphIterationToFindLeafs() { String drl = "import " + Datum.class.getCanonicalName() + ";\n" + "import java.util.List;\n" + "query findLeafs(Datum datum, List results)\n" + " ( eval( datum.getChildren().size() == 0 ) and \n" + " eval( results.add ( datum ) ) )\n" + " or \n" + " ( eval( datum.getChildren().size() != 0 ) and \n" + " child : Datum( ) from datum.children and\n" + " findLeafs( child, results; ) ) \n" + "end\n"; System.out.println( drl ); KnowledgeBase knowledgeBase = loadKnowledgeBaseFromString( drl ); StatefulKnowledgeSession ksession = knowledgeBase.newStatefulKnowledgeSession(); List<Datum> list = new ArrayList<Datum>(); Datum d1 = new Datum("d1"); Datum d2 = new Datum("d2"); Datum d3 = new Datum("d3"); Datum d4 = new Datum("d4"); Datum d5 = new Datum("d5"); Datum d6 = new Datum("d6"); Datum d7 = new Datum("d7"); d1.getChildren().add( d2 ); d1.getChildren().add( d3 ); d3.getChildren().add( d4 ); d3.getChildren().add( d5 ) ; d5.getChildren().add( d6 ) ; d6.getChildren().add( d7 ) ; ksession.getQueryResults("findLeafs", d1, list); System.out.println( list ); } public static class Datum { private String description; private List<Datum> children; public Datum(String description) { this.description = description; children = new ArrayList<Datum>(); } public String getDescription() { return description; } public void setDescription(String description) { this.description = description; } public List<Datum> getChildren() { return children; } @Override public String toString() { return "Datum{" + "description='" + description + '\'' + '}'; } } On 18 Jun 2014, at 18:44, Borris <borris(a)chaos.org.uk&gt; wrote: