A composite key is a primary key that consists of more than one attribute. A composite attribute is an attribute that can be subdivided to yield attributes for each of its components. If the ER diagram contains the attribute names for each of its entities, a composite key is indicated in the ER diagram by the fact that more than one attribute name is underlined to indicate its participation in the primary key. There is no ER convention that enables you to indicate that an attribute is a composite attribute.