Thanks for the reply. Maybe you could give me some example how to do that?
I've got 4 buildings:
Each building has 4 rooms:
Room code is unique only within a particular building:
1A, 1B, 1C, 1D.
2A, 2B, 2C, 2D.
3A, 3B, 3C, 3D.
4A, 4B, 4C, 4D.
How can I make a constraint from this?