creates
a message pointing toward the second classifier role in the link.
creates
a link message pointing in the other direction.Like classifier and association roles, messages can be <Unspecified>, meaning that they are abstract and not realizations of class operations. Link messages can be instances of existing operations of a class or instances of new operations. However, for a link message to realize some operation, the operation must be a method of the class associated with the target of the message.
Messages, whether abstract or instances of operations, have the notation ReturnValue = MessageName(Arg, Arg, Arg...). You can use this notation in the message name when you first create it, or you can enter these boxes explicitly in the Features window.
A message that is an instance of an operation does not necessarily show the form of the actual call. You can specify just the items of interest in the collaboration. The ReturnValue is optional; the function might not return a value, or you might not want to specify the local variable to which the return value applies.
By default, the new message is <Unspecified>. To make it an instance of a new or existing operation of the target class or actor, open its Features window (see Modifying the features of a message.