ERM: Key attribute for relation <p>My question is the following: Can relations have key attributes like shown in the following figure? <a href="https://i.stack.imgur.com/il3tg.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/il3tg.png" alt=""></a></p> <p>For me it doesn't make sense, however I have found them like in <a href="https://i.stack.imgur.com/il3tg.png" rel="nofollow noreferrer">1</a>. If it is possilbe, how should I "resolve" them in the relational schema?</p> <p>I found a similar the question on [2] but it seems to focus on how to handle attributes during the transformation of the ERM to the relational schema.</p> <p><a href="https://i.stack.imgur.com/il3tg.png" rel="nofollow noreferrer">1</a> <a href="https://www.wu.ac.at/fileadmin/wu/_processed_/csm_erm_cardinalities2_84a65dbc2b.png" rel="nofollow noreferrer">https://www.wu.ac.at/fileadmin/wu/<em>processed</em>/csm_erm_cardinalities2_84a65dbc2b.png</a></p> <p>[2] <a href="http://stackoverflow.com/questions/9700196/relationship-attributes-in-er-diagrams">relationship attributes in ER diagrams</a></p>