The operation name is used to select the target Operation with the given name. The operation arguments become argument Expressions on the Action. Within a sequence diagram the existence and duration of the object in a role is shown, but the relationships among the roles is not shown. There are ClassifierRoles and AssociationRoles. A message is shown as a horizontal solid arrow from the lifeline of one object to the lifeline of another object.
Time flows from the top of the page downward.
Unless specifically annotated, only the sequence of messages is shown, not the exact time. A message can be seen as transition instance and may be given a name. This name may be used in constraint expressions to designate the time the message was sent. If the message line is slanted, then the primed-name indicates the time at which the message is received. Constraints may be specified by placing Boolean expressions in braces on the sequence diagram.