I'm sorry, I still don't quite understand. I will give an example (without revealing too much about my ER diagram): If I have a relationship 'Makes' between Client and Booking, and I want the PK in the Booking table to include clientID, would I put 'clientID {PK}' (perhaps as well as some other attribute to make a composite key) as an attribute despite clientID being a foreign key? If I do not include it then the it will be impossible to make a unique PK as someone else may make the same booking on the same day. We have been explicitly told in lectures and in these forums that we should NOT include FKs as attributes (in the attribute data dictionary/ER diagram) as they are implied by the relationships, but sometimes they are required to make a unique PK.