diff -r c9e3cfbbe4ad -r 1a58b78a8f99 src/pyams_utils/interfaces/site.py
--- a/src/pyams_utils/interfaces/site.py	Thu Mar 08 09:13:06 2018 +0100
+++ b/src/pyams_utils/interfaces/site.py	Sat Mar 10 01:58:45 2018 +0100
@@ -41,10 +41,11 @@
 class ISiteGenerations(Interface):
     """Site generations interface"""
 
+    order = Attribute("Order in which generations should be upgraded")
     generation = Attribute("Current schema generation")
 
     def evolve(self, site, current=None):
-        """Evolve from current generation to last one"""
+        """Evolve database from current generation to last one"""
 
 
 class IStaticConfigurationManager(IAttributeAnnotatable):