Well if the combination of attributes makes up the primary key, then it would be a composite primary key so you would show it as the key. It just also gets partially used by another table as the foreign key so it would just not be labelled as the foreign key, I wouldn't remove it as such. I found this while searching if it helps: key - a minimal set of attributes that uniquely identifies a record (or row) primary key - a single attribute that (a) cannot be null, and (b) uniquely identifies a row. composite key - two or more attributes that, taken together, uniquely identifies a record (or row) foreign key - an attribute in a table that references the primary key in another table. Can be part of a composite key. (Could also be a primary key, though this would mean the 2 entities/tables should be logically combined.) https://opentextbc.ca/dbdesign01/chapter/chapter-8-entity-relationship-model/