diff --git a/README.txt b/README.txt
index 9f2ae04..f99ac5b 100755
--- a/README.txt
+++ b/README.txt
@@ -1,6 +1,12 @@
-# $Id$
+loops - Linked Objects for Organizational Process Services
+==========================================================
 
-Task Examples::
+  ($Id$)
+
+Tasks and Subtasks
+~~~~~~~~~~~~~~~~~~
+
+Let's start with creating a few example tasks:
 
     >>> from loops.task import Task
     >>> t1 = Task()
@@ -11,3 +17,36 @@ Task Examples::
     >>> t2.title
     u'Second Task'
 
+Now we want to make the second task a subtask of the first one.
+
+In order to do this we first have to provide a relations registry. For
+testing we use a simple dummy implementation.
+
+    >>> from cybertools.relation.interfaces import IRelationsRegistry
+    >>> from cybertools.relation.registry import DummyRelationsRegistry
+    >>> from zope.app.testing import ztapi
+    
+    >>> ztapi.provideUtility(IRelationsRegistry, DummyRelationsRegistry())
+
+Now we can assign the task t2 as a subtask to t1:
+        
+    >>> t1.assignSubtask(t2)
+
+We can now ask our tasks for their subtasks and parent tasks:
+
+    >>> st1 = t1.getSubtasks()
+    >>> len(st1)
+    1
+    >>> t2 in st1
+    True
+    >>> len(t1.getParentTasks())
+    0
+        
+    >>> pt2 = t2.getParentTasks()
+    >>> len(pt2)
+    1
+    >>> t1 in pt2
+    True
+    >>> len(t2.getSubtasks())
+    0
+    
\ No newline at end of file
diff --git a/relation.py b/relation.py
deleted file mode 100644
index 91843fa..0000000
--- a/relation.py
+++ /dev/null
@@ -1,47 +0,0 @@
-#
-#  Copyright (c) 2004 Helmut Merz helmutm@cy55.de
-#
-#  This program is free software; you can redistribute it and/or modify
-#  it under the terms of the GNU General Public License as published by
-#  the Free Software Foundation; either version 2 of the License, or
-#  (at your option) any later version.
-#
-#  This program is distributed in the hope that it will be useful,
-#  but WITHOUT ANY WARRANTY; without even the implied warranty of
-#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-#  GNU General Public License for more details.
-#
-#  You should have received a copy of the GNU General Public License
-#  along with this program; if not, write to the Free Software
-#  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
-#
-
-"""
-relation classes implementation.
-
-$Id$
-"""
-
-from BTrees.OOBTree import OOSet
-from zope.interface import implements
-from zope.app import zapi
-
-from interfaces import IRelation, IRelations
-
-
-class Relation(object):
-
-    implements(IRelation)
-
-    def __init__(self, source, target):
-        self._source = source
-        self._target = target
-
-
-class Relations(OOSet):
-
-    implements(IRelations)
-
-    def add(self, relation, **kw):
-        self.insert(relation)
-
diff --git a/task.py b/task.py
index a15d0d2..f51c27b 100644
--- a/task.py
+++ b/task.py
@@ -27,14 +27,24 @@ from zope.app.container.ordered import OrderedContainer
 from zope.app.copypastemove import ObjectCopier
 from zope.app import zapi
 from zope.schema.fieldproperty import FieldProperty
+from zope.component.interfaces import IFactory
 
-from relation import Relation, Relations
+from cybertools.relation.interfaces import IRelationsRegistry
+from cybertools.relation import DyadicRelation
+
+#from relation import Relation, Relations
 from resource import Resource
 from interfaces import ITask
 
 from copy import copy
 
 
+class SubtaskRelation(DyadicRelation):
+    """ Relation of a first task (the parent task) to a second task
+        (the subtask).
+    """
+
+
 class Task(OrderedContainer):
 
     implements(ITask)
@@ -53,19 +63,22 @@ class Task(OrderedContainer):
     # subtasks:
 
     def getSubtasks(self, taskTypes=None):
-        st = [ r._target for r in self._subtasks ]
-        st.sort(lambda x,y: x.priority < y.priority and -1 or 1)
-        return tuple(st)
+        registry = zapi.getUtility(IRelationsRegistry)
+        return [r.second
+                for r in registry.query(relationship=SubtaskRelation,
+                                        first=self)]
+        # TODO: sort according to priority
 
     def getParentTasks(self, taskTypes=None):
-        pt = [ r._source for r in self._parentTasks ]
-        return tuple(pt)
+        registry = zapi.getUtility(IRelationsRegistry)
+        return [r.first
+                for r in registry.query(relationship=SubtaskRelation,
+                                        second=self)]
 
     def assignSubtask(self, task):
-        if task not in self.getSubtasks():
-            rel = Relation(self, task)
-            self._subtasks.add(rel)
-            task._parentTasks.add(rel)
+        registry = zapi.getUtility(IRelationsRegistry)
+        registry.register(SubtaskRelation(self, task))
+        # TODO (?): avoid duplicates
 
     def createSubtask(self, taskType=None, container=None, name=None):
         container = container or zapi.getParent(self)
diff --git a/test_task.py b/test_task.py
index 453c702..a9b7052 100755
--- a/test_task.py
+++ b/test_task.py
@@ -30,23 +30,6 @@ class TestTask(unittest.TestCase):
 
     # the tests...
 
-    def testInterface(self):
-        self.assert_(ITask.providedBy(Task()),
-            'Interface ITask is not implemented by class Task.')
-        self.assert_(IContained.providedBy(Task()),
-            'Interface IContained is not implemented by class Task.')
-        verifyClass(ITask, Task)
-
-    def testContained(self):
-        self.assertEqual(u'tsk1', zapi.name(self.t1))
-        self.assertEqual(u'f1', zapi.name(zapi.getParent(self.t1)))
-
-    def testTitle(self):
-        t = Task()
-        self.assertEqual(u'', t.title)
-        t.title = u'First Task'
-        self.assertEqual(u'First Task', t.title)
-
     def testQualifier(self):
         t = Task()
         self.assertEqual(u'', t.qualifier)