diff --git a/storlets/gateway/common/file_manager.py b/storlets/gateway/common/file_manager.py
index 18608c4e..d9621dc6 100644
--- a/storlets/gateway/common/file_manager.py
+++ b/storlets/gateway/common/file_manager.py
@@ -12,9 +12,10 @@
 # implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+import abc
 
 
-class FileManager(object):
+class FileManager(object, metaclass=abc.ABCMeta):
     """
     This class is used to load/save files required for storlet execution
     from/into the storage which also stores data to be processed
@@ -23,22 +24,25 @@ class FileManager(object):
     def __init__(self):
         pass
 
+    @abc.abstractmethod
     def get_storlet(self, name):
         """
         Load storlet file content
 
         :param name: storlet file name
         """
-        raise NotImplementedError()
+        pass
 
+    @abc.abstractmethod
     def get_dependency(self, name):
         """
         Load dependency file content
 
         :param name: dependency file name
         """
-        raise NotImplementedError()
+        pass
 
+    @abc.abstractmethod
     def put_log(self, name, fobj):
         """
         Save storlet log file to storage
@@ -46,4 +50,4 @@ class FileManager(object):
         :param name: log file name
         :param data_iter: File Object
         """
-        raise NotImplementedError()
+        pass
diff --git a/storlets/sbus/datagram.py b/storlets/sbus/datagram.py
index 4b29f8e2..5f8206dd 100644
--- a/storlets/sbus/datagram.py
+++ b/storlets/sbus/datagram.py
@@ -12,6 +12,7 @@
 # implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+import abc
 import copy
 import json
 
@@ -47,14 +48,15 @@ class SBusFileDescriptor(object):
         return cls(fdtype, fileno, storlets_metadata, storage_metadata)
 
 
-class SBusDatagram(object):
+class SBusDatagram(object, metaclass=abc.ABCMeta):
     """
     The manager class for the datagram passed over sbus protocol
     """
 
-    # Each child Datagram should define what fd types are expected with
-    # list format
-    _required_fdtypes = None
+    @property
+    @abc.abstractmethod
+    def _required_fdtypes(self):
+        pass
 
     def __init__(self, command, sfds, params=None, task_id=None):
         """
@@ -67,9 +69,6 @@ class SBusDatagram(object):
         :param task_id: An optional string task id. This is currently used for
                         cancel command
         """
-        if type(self) == SBusDatagram:
-            raise NotImplementedError(
-                'SBusDatagram class should not be initialized as bare')
         self.command = command
         fdtypes = [sfd.fdtype for sfd in sfds]
         self._check_required_fdtypes(fdtypes)
@@ -145,11 +144,6 @@ class SBusDatagram(object):
             return ret[0]
 
     def _check_required_fdtypes(self, given_fdtypes):
-        if self._required_fdtypes is None:
-            raise NotImplementedError(
-                'SBusDatagram class should define _required_fdtypes')
-        # the first len(self._required_fdtypes) types should be fit
-        # to the required list
         if given_fdtypes[:len(self._required_fdtypes)] != \
                 self._required_fdtypes:
             raise ValueError('Fd type mismatch given_fdtypes:%s \
@@ -178,7 +172,9 @@ class SBusServiceDatagram(SBusDatagram):
      - SBUS_CMD_PING
      - SBUS_CMD_CANCEL
     """
-    _required_fdtypes = [sbus_fd.SBUS_FD_SERVICE_OUT]
+    @property
+    def _required_fdtypes(self):
+        return [sbus_fd.SBUS_FD_SERVICE_OUT]
 
     def __init__(self, command, sfds, params=None, task_id=None):
         super(SBusServiceDatagram, self).__init__(
@@ -190,11 +186,16 @@ class SBusServiceDatagram(SBusDatagram):
 
 
 class SBusExecuteDatagram(SBusDatagram):
-    _required_fdtypes = [sbus_fd.SBUS_FD_SERVICE_OUT,
-                         sbus_fd.SBUS_FD_INPUT_OBJECT,
-                         sbus_fd.SBUS_FD_OUTPUT_OBJECT,
-                         sbus_fd.SBUS_FD_OUTPUT_OBJECT_METADATA,
-                         sbus_fd.SBUS_FD_LOGGER]
+
+    @property
+    def _required_fdtypes(self):
+        return [
+            sbus_fd.SBUS_FD_SERVICE_OUT,
+            sbus_fd.SBUS_FD_INPUT_OBJECT,
+            sbus_fd.SBUS_FD_OUTPUT_OBJECT,
+            sbus_fd.SBUS_FD_OUTPUT_OBJECT_METADATA,
+            sbus_fd.SBUS_FD_LOGGER
+        ]
 
     def __init__(self, command, sfds, params=None, task_id=None):
         # TODO(kota_): the args command is not used in ExecuteDatagram
diff --git a/tests/unit/sbus/test_datagram.py b/tests/unit/sbus/test_datagram.py
index fa8b083a..8a932835 100644
--- a/tests/unit/sbus/test_datagram.py
+++ b/tests/unit/sbus/test_datagram.py
@@ -16,7 +16,7 @@
 import json
 import unittest
 import storlets.sbus.file_description as sbus_fd
-from storlets.sbus.datagram import SBusFileDescriptor, SBusDatagram, \
+from storlets.sbus.datagram import SBusFileDescriptor, \
     SBusServiceDatagram, SBusExecuteDatagram, build_datagram, \
     build_datagram_from_raw_message
 from storlets.sbus.command import SBUS_CMD_PING, SBUS_CMD_EXECUTE
@@ -53,27 +53,6 @@ class TestSBusFileDescriptor(unittest.TestCase):
                          fd.storage_metadata)
 
 
-class TestSBusDatagram(unittest.TestCase):
-    def test_check_required_fdtypes_not_implemented(self):
-        # SBusDatagram designed not to be called independently
-        with self.assertRaises(NotImplementedError) as err:
-            SBusDatagram('', [], [])
-        self.assertEqual(
-            'SBusDatagram class should not be initialized as bare',
-            err.exception.args[0])
-
-    def test_invalid_child_class_definition(self):
-        # no definition for _required_fdtypes
-        class InvalidSBusDatagram(SBusDatagram):
-            pass
-
-        with self.assertRaises(NotImplementedError) as err:
-            InvalidSBusDatagram('', [], [])
-        self.assertEqual(
-            'SBusDatagram class should define _required_fdtypes',
-            err.exception.args[0])
-
-
 class SBusDatagramTestMixin(object):
     def setUp(self):
         self.params = {'param1': 'paramvalue1'}