An Improved Sequence Diagram

Let us try to improve the simple sequence diagram.
# Object definition
object(S,"s:Switch");
object(P,"p:Pump");
step();
active(S);
active(P);

# Message exchange
message(S,P,"run()");
message(S,P,"stop()");

# Object lifeline completion
step();
complete(S);
complete(P);
Here, we have manually advanced the timeline of our diagrams with a step(); call after we defined the objects, to provide them with a bit of breathing space. We also added a similar step call at the end of the diagram. Finally, we made both objects active, after their definition. Calling active on a given object will change the drawing of its lifeline, from the dashed format indicating an inactive object, to a thick swimming-lane, active object, format.

The resultant diagram is
Improved sequence diagram

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