Ana M. Fernández

 A UML diagram that depicts: ◦ interactions between objects. ◦ how the business currently works by showing how various business objects interact.  Purpose: 1. Model flow of control 2. Identify synchronization 3. Illustrate typical scenarios

 The focus is less on messages themselves and more on the order in which messages occur.  The diagram conveys this information along 2 dimensions: ◦ the vertical dimension shows, top down, the time sequence of messages/calls as they occur, ◦ the horizontal dimension shows, left to right, the object instances that the messages are sent to.

 Instance Name : Class Name ◦ Underlined  specific instance (Bill, Fred) ◦ Not underlined  kind of instance or role (buyer, seller)

 Message =a line to the receiving object with: ◦ a solid arrowhead (if a synchronous call operation) ◦ a stick arrowhead (if an asynchronous signal)  The message/method name is placed above the arrowed line.  Return message = dotted line with an open arrowhead back to the originating lifeline (above the return value from the operation).

 To model mutually exclusive choice between two or more message sequences (if then else)  The word "alt" is placed inside the frame's namebox.  Operands are separated by a dashed line.

 To model a sequence that, given a certain condition, will occur; otherwise, the sequence does not occur (If then).  The word “opt" is placed inside the frame's namebox.

 To model a repetitive sequence.  The word “loop" is placed inside the frame's namebox (add the minimum and maximum of iterations)

 To model parallel processing activities.  The word “par" is placed inside the frame's namebox.  Break up the frame  horizontal operands separated by a dashed line.

 Messages: ◦ Synchronous ◦ Asynchronous ◦ Return  Alternative  Option  Loop  Pararell