crazy change?.diff

diff --git a/StorletSamples/python/simple/simple.py b/StorletSamples/python/simple/simple.py
index df5d807..740b708 100644
--- a/StorletSamples/python/simple/simple.py
+++ b/StorletSamples/python/simple/simple.py
@@ -13,8 +13,37 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+class StorletAppTemplate(object):
+    def __call__(self, in_md, in_files, out_md_files, out_files, params):
+        """
+        :param in_md: a dict of input metadata (why this is just a dict?)
+        :param in_files: a list of input file objects to read
+        :param out_md_files: a list of md??? <- why we need this as a list?
+        :param out_files: a list of file-like objects to write
+        :param params: a dict of query_args
+        """
+        out_md, out_files = self.invoke(in_md, in_files)
+        out_md_files[0].write(json.dumps(out_md))
+        out_md_files[0].close()
+        # translation from out_files from invoke to out_files for upper abstraction
+        # TODOTODOTOD
+
 
-class SimpleStorlet(object):
+    def invoke(self, in_md, in_files, params):
+        """
+        All storlet app should implement this invocation method
+        :param in_md: a dict of input metadata (why this is just a dict?)
+        :param in_files: a list of input file objects to read
+        :param out_md_files: a list of md??? <- why we need this as a list?
+        :param out_files: a list of file-like objects to write
+        :param params: a dict of query_args
+
+        :return: a tuple of (out_md, out_files)
+        """
+        raise NotImplementedError()
+
+
+class SimpleStorlet(StorletAppTemplate):
     def __init__(self, logger):
         self.logger = logger
 
@@ -26,7 +55,12 @@ class SimpleStorlet(object):
         # TODO(takashi): This is just for drafting interface
         raise NotImplementedError()
 
-    def __call__(self, in_md, in_files, out_md_files, out_files, params):
+    def invoke(self, in_md, in_files, params):
+        """
+        :param in_md: a dict of input metadata (why this is just a dict?)
+        :param in_files: a list of input file objects to read
+        :param params: a dict of query_args
+        """
         self.logger.debug('Returning metadata')
         metadata = in_md[0]
         metadata['test'] = 'simple'
@@ -48,3 +82,4 @@ class SimpleStorlet(object):
         self.logger.debug('Complete')
         in_files[0].close()
         out_files[0].close()
+        return out_md_files, out_files  # out_md_files should be out_md dict?