A sequence diagram is defined in three main phases:

1. Object definition
2. Message exchange
3. Object lifeline completion

The following is an example of a very simple UMLGraph sequence diagram (from now on we will ommit the `.PS/.PE` and `copy "sequence.pic";` elements.) .PS copy "sequence.pic"; # Object definition object(S,"s:Switch"); object(P,"p:Pump"); # Message exchange message(S,P,"run()"); message(S,P,"stop()"); # Object lifeline completion complete(S); complete(P); .PE The above code, defines two objects, S and P, labeled as "s:Switch" and "p:Pump". Objects are placed in the diagram from left to right, in the order they are defined. All defined objects are initially inactive.

The code then sends a messages from S to P labeled "run()", and another one labeled "stop()". Each message automatically advances the sequence diagram timeline by a single step.

Finally, the code completes the lifelines of the two objects.

The resultant diagram is

Simple sequence diagram