--- a/schema.py	Thu Jul 04 09:26:59 2013 +0200
+++ b/schema.py	Tue Jul 30 20:31:57 2013 +0200
@@ -93,7 +93,7 @@
                       'WorkflowTransition', 'BaseTransition',
                       'SubWorkflowExitPoint'))
 
-INTERNAL_TYPES = set(('CWProperty', 'CWCache', 'ExternalUri',
+INTERNAL_TYPES = set(('CWProperty', 'CWCache', 'ExternalUri', 'CWDataImport',
                       'CWSource', 'CWSourceHostConfig', 'CWSourceSchemaConfig'))
 
 
@@ -739,6 +739,9 @@
             return self.expression == other.expression
         return False
 
+    def __hash__(self):
+        return hash(self.expression)
+
     def __deepcopy__(self, memo):
         return self.__class__(self.expression, self.mainvars)
     def __getstate__(self):