PlantUML Activity Diagram: Branching and Loops

Activity Diagram Branching and Loops

Activity diagrams model workflows and business processes. PlantUML uses a concise text syntax for activities, decisions, and flow control.

Basic Activity

@startuml
start
:Receive request;
:Validate input;
:Process data;
:Return response;
stop
@enduml

Activities are written between colons and semicolons: :Activity name;. The start and stop keywords create the filled circle and bull's-eye terminators.

If/Else Branching

if (Is user authenticated?) then (yes)
  :Load dashboard;
else (no)
  :Redirect to login;
  :Show login form;
endif

Nested Conditions

if (Payment method?) then (credit card)
  :Charge card;
  if (Charge successful?) then (yes)
    :Confirm order;
  else (no)
    :Show error;
  endif
elseif (PayPal) then
  :Redirect to PayPal;
else (bank transfer)
  :Generate invoice;
endif

While Loops

while (More items to process?) is (yes)
  :Process next item;
  :Update progress;
endwhile (no)

Parallel Processing (Fork/Join)

fork
  :Send email notification;
fork again
  :Update database;
fork again
  :Push to message queue;
end fork

The fork/fork again/end fork block shows activities that execute concurrently. All branches must complete before the flow continues past end fork.

Swim Lanes

|Customer|
start
:Place order;
|Warehouse|
:Pick items;
:Pack shipment;
|Shipping|
:Generate label;
:Ship package;
|Customer|
:Receive delivery;
stop

Swim lanes partition activities by responsible party using pipe characters.