diff --git a/organize/README.txt b/organize/README.txt
index 30c77b0..5b64ed5 100644
--- a/organize/README.txt
+++ b/organize/README.txt
@@ -1,8 +1,12 @@
+==================================================
 Organizations: Persons, Institutions, Addresses...
 ==================================================
 
   ($Id$)
 
+Persons and Addresses
+=====================
+
 Let's start with a Person:
 
   >>> from cybertools.organize.party import Person
@@ -17,7 +21,7 @@ Let's start with a Person:
   {}
 
 A Person object knows the age of the person:
-  
+
   >>> john.age is None
   True
   >>> from datetime import date
@@ -43,3 +47,8 @@ Let's create an address and assign it to a person:
   >>> john.addresses['standard'].street
   u'Broadway 1'
 
+
+Service Management
+==================
+
+  >>> from cybertools.organize.service import ServiceInstance
diff --git a/organize/interfaces.py b/organize/interfaces.py
index 774c5c5..a13533c 100644
--- a/organize/interfaces.py
+++ b/organize/interfaces.py
@@ -1,5 +1,5 @@
 #
-#  Copyright (c) 2006 Helmut Merz helmutm@cy55.de
+#  Copyright (c) 2007 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
@@ -17,7 +17,7 @@
 #
 
 """
-Interfaces for organizational stuff like persons, addresses, tasks, ...
+Interfaces for organizational stuff like persons, addresses, tasks, services...
 
 $Id$
 """
@@ -29,11 +29,15 @@ from zope.i18nmessageid import MessageFactory
 _ = MessageFactory('zope')
 
 
+# schema fields
+
 class SimpleList(schema.List): pass
 
 class LinesList(schema.List): pass
 
 
+# persons, addresses, ...
+
 class IPerson(Interface):
     """ Resembles a human being with a name (first and last name),
         a birth date, and a set of addresses.
@@ -65,7 +69,7 @@ class IPerson(Interface):
                     title=_(u'Age'),
                     description=_(u'The current age in full years'),
                     readonly=True)
-    
+
     addresses = Attribute('A mapping whose values provide the IAddress '
                           'interface')
 
@@ -98,6 +102,8 @@ class IAddress(Interface):
                     required=False,)
 
 
+# tasks
+
 class ITask(Interface):
     """ A task has a start date, an optional end date, and is usually
         assigned to one or more persons.
@@ -113,3 +119,81 @@ class ITask(Interface):
                                    'finished'),
                     required=False,)
 
+
+# services
+
+
+class IService(Interface):
+    """ A general service definition or a group of service instances,
+        e.g. a regular bus service or a series of trainings.
+    """
+
+
+class IServiceInstance(Interface):
+    """ A concrete service instance that clients may register with.
+    """
+
+    service = Attribute('The service this object is an instance of.')
+
+    seats = schema.Int(
+                    title=_(u'Number of Seats'),
+                    description=_(u'The capacity (maximum number of clients) '
+                        'of this service; a negative number means: '
+                        'no restriction, i.e. unlimited capacity.'),
+                    required=False,)
+
+    availableSeats = Attribute('Available capacity, i.e. number of seats '
+                        'still available; a negative number means: '
+                        'no restriction, i.e. unlimited capacity. '
+                        'Read-only attribute')
+
+    serviceProviders = Attribute('A collection of one or more service providers.')
+
+    resources = Attribute('A collection of one or more resources.')
+
+    registrations = Attribute('A collection of client registrations.')
+
+    def register(client):
+        """ Register a client with this service. Return an IRegistration
+            object if the registration is successful, otherwise
+            (e.g. if no seat is available) return None.
+        """
+
+
+class IScheduledServiceInstance(IServiceInstance):
+    """ A service instance that starts at a certain date/time and
+        usually ends a certain time later.
+    """
+
+    start = schema.Date(
+                    title=_(u'Start date/time'),
+                    description=_(u'The date/time when the service starts'),
+                    required=False,)
+    end = schema.Date(
+                    title=_(u'End date/time'),
+                    description=_(u'The date/time when the service ends'),
+                    required=False,)
+
+    duration = Attribute('Time delta between start and end date/time.')
+
+
+class IRegistration(Interface):
+    """ Information about the registration of a client with a service.
+    """
+
+    client = Attribute('The client registered')
+
+
+class IResource(Interface):
+    """ A resource is needed by a service to be able to work, e.g. a
+        room or a bus. A resource may have a limited capacity so that
+        at a certain time it may only be used by services to certain
+        extent.
+    """
+
+
+class IServiceProvider(Interface):
+    """ An entity, e.g. a person or an institution, that is responsible
+        for providing a service or a service instance.
+    """
+
diff --git a/storage/filesystem.py b/storage/filesystem.py
index 5664aa5..68b1027 100644
--- a/storage/filesystem.py
+++ b/storage/filesystem.py
@@ -67,6 +67,10 @@ class FileSystemStorage(object):
         f.close()
         return data
 
+    def getUniqueAddress(self, address, params={}):
+        subDir = params.get('subdirectory')
+        return self.getDir(address, subDir)
+
 
 class FSSDataManager(object):
 
diff --git a/storage/interfaces.py b/storage/interfaces.py
index a8fe14c..cfeef32 100644
--- a/storage/interfaces.py
+++ b/storage/interfaces.py
@@ -27,11 +27,15 @@ from zope.interface import Interface, Attribute
 
 class IStorageInfo(Interface):
     """ Provides information about the storage of an object.
+        Used typically as an adapter.
     """
 
     storageName = Attribute('Name of a utility that is used for storage of the object')
     storageParams = Attribute('Dictionary with storage parameters, e.g. a '
                         'directory name')
+    externalAddress = Attribute('Relative address within the external storage')
+    uniqueAddress = Attribute('Full address that uniquely identifies the object. '
+                              'Read-only')
 
 
 class IExternalStorage(Interface):
@@ -53,3 +57,8 @@ class IExternalStorage(Interface):
     # TODO: provide file and/or iterator access methods
     # read, write, close, __iter__
 
+    def getUniqueAddress(address, params=None):
+        """ Return a unique (complete) address of the object that may
+            be used to check if two addresses reference the same external
+            object.
+        """