diff -r 38a4e83c8160 -r ade319674170 schema.py
--- a/schema.py	Tue Aug 04 18:58:54 2009 +0200
+++ b/schema.py	Tue Aug 04 19:36:22 2009 +0200
@@ -516,6 +516,11 @@
     def __init__(self, restriction):
         self.restriction = restriction
 
+    def check_consistency(self, subjschema, objschema):
+        if objschema.is_final():
+            raise BadSchemaDefinition("unique constraint doesn't apply to "
+                                      "final entity type")
+
     def serialize(self):
         return self.restriction