@Override
 public boolean containsKey(Object key) {
   if (key == null) return false;
   if (!(key instanceof Namespace)) return false;
   Namespace prefix = (Namespace) key;
   if (prefix.compareTo(from) < 0) return false;
   if (prefix.compareTo(to) >= 0) return false;
   BerkeleyDBDelegateTreeNodeEntity.PrimaryKeyData pk =
       new BerkeleyDBDelegateTreeNodeEntity.PrimaryKeyData(parent.getStatementUuid(), prefix);
   return transaction.contains(index, pk);
 }
 @Override
 public DelegateTreeSubNode get(Object key) {
   if (key == null) return null;
   if (!(key instanceof Namespace)) return null;
   Namespace prefix = (Namespace) key;
   if (prefix.compareTo(from) < 0) return null;
   if (prefix.compareTo(to) >= 0) return null;
   BerkeleyDBDelegateTreeNodeEntity.PrimaryKeyData pk =
       new BerkeleyDBDelegateTreeNodeEntity.PrimaryKeyData(parent.getStatementUuid(), prefix);
   BerkeleyDBDelegateTreeNodeEntity entity = transaction.get(index, pk);
   if (entity == null) return null;
   return (DelegateTreeSubNode) persistenceManager.entityToDelegateTreeNode(entity);
 }
 @Override
 public CloseableSortedMap<Namespace, DelegateTreeSubNode> tailMap(Namespace fromKey) {
   return new BerkeleyDBLocalDelegateTreeSubNodeMap(
       persistenceManager, transaction, parent, from.max(fromKey), to);
 }
 @Override
 public CloseableSortedMap<Namespace, DelegateTreeSubNode> headMap(Namespace toKey) {
   return new BerkeleyDBLocalDelegateTreeSubNodeMap(
       persistenceManager, transaction, parent, from, to.min(toKey));
 }