Information Modeling and Relational Databases, 2nd Edition

9.4. Associations

UML uses Boolean attributes instead of unary relationships, but allows relationships of all other arities. Optionally, each association may be given at most one name. Association names normally start with a capital letter. Binary associations are depicted as lines between classes. Association lines may include elbows to assist with layout or when needed (e.g., for ring relationships). Association roles appear simply as line ends instead of boxes, but may be given role names. Once added, role names may not be suppressed. Verbalization into sentences is possible only for infix binaries, and then only by naming the association with a predicate reading (e.g., “Employs”) and using an optional marker “▸” to denote the direction. ...