//and its children
Set<String> children = nodeRefs.get(key);
Iterator<String> childrenIt = children.iterator();
while(childrenIt.hasNext()){
String child = childrenIt.next();
if(!dg.containsVertex(child)) {
dg.addVertex(child);
}
//add edge, precondition: vertex key - child are already added to the graph
Edge de = def.createEdge(key, child);
dg.addEdge(de);