BPMN sub processes

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A sub-process is an activity containing its own process. Collapsed, it keeps the parent diagram readable; expanded, it shows the detail.

It is the main tool for keeping a real process on one page.

#When it matters

  • Processes too large to read on one screen.

  • Reusable fragments that appear in several processes.

#The symbols

Symbol

Means

Collapsed sub-process

Task with a plus marker. Detail lives elsewhere.

Expanded sub-process

Drawn inline in a box, for shorter detail.

Call activity

Thick border. Calls a process defined separately, and reusable.

Event sub-process

Dotted border. Triggered by an event rather than by flow.

Transaction

Double border. All or nothing, with compensation.

#A few things that catch people out

  • A call activity is reusable; an ordinary sub-process is not. The distinction matters when automating.

  • Event sub-processes have no incoming sequence flow; they are triggered, not entered.

  • Collapse anything that is not the subject of this diagram.

Sequence flow stays inside the pool.