diff -r a747e211266b -r ab626726a70a schema.py
--- a/schema.py	Tue Nov 03 18:03:21 2015 +0100
+++ b/schema.py	Tue Nov 03 18:10:58 2015 +0100
@@ -105,6 +105,9 @@
 INTERNAL_TYPES = set(('CWProperty', 'CWCache', 'ExternalUri', 'CWDataImport',
                       'CWSource', 'CWSourceHostConfig', 'CWSourceSchemaConfig'))
 
+UNIQUE_CONSTRAINTS = ('SizeConstraint', 'FormatConstraint',
+                      'StaticVocabularyConstraint',
+                      'RQLVocabularyConstraint')
 
 _LOGGER = getLogger('cubicweb.schemaloader')