What is a Sub-Process in BPMN?

A Sub-Process is a compound activity containing its own complete BPMN flow. It groups related activities, provides variable scope, and enables boundary events to handle exceptions at the group level.

When should I use a Sub-Process?

Use Sub-Processes to group related activities, scope variables, attach boundary events for exception handling, or create multi-instance loops. They improve readability and enable process decomposition.

How is the Sub-Process different from related elements?

Sub-Processes contain embedded flows visible in the diagram. Call Activities invoke external reusable processes. Tasks are atomic. Sub-Processes provide local scope; Call Activities share global process definitions.

activities

Sub-Process

A Sub-Process is a compound activity containing its own complete flow of activities, gateways, and events. It encapsulates related steps, enabling process decomposition and reuse. For example, an "Order Fulfillment" sub-process groups pick, pack, and ship steps together, allowing a single error boundary event to handle failures for all three steps at once.

What is a Sub-Process?

A Sub-Process (or Embedded Sub-Process) contains a complete BPMN flow within it-activities, gateways, events, and sequence flows. It groups related activities together, providing scope for variables and event handling.

Visual Representation

A Sub-Process displays as a large rounded rectangle with a small plus sign at the bottom center when collapsed, or shows its internal contents when expanded. The border is thicker than regular tasks.

Key Characteristics

Contains complete flow: Has its own start event, activities, and end event(s)
Variable scope: Can define local variables visible only within the sub-process
Event scope: Boundary events can attach to handle sub-process-level exceptions
Visual grouping: Organizes related activities for readability

See it in action

Visa application steps are grouped into a reusable sub-process

Read: The Travel Agency →

Common mistake

Making sub-processes too large. If a sub-process has more than 7-10 elements, consider breaking it into smaller sub-processes or using call activities.

How it connects

Call ActivityUse a Call Activity when the sub-process needs to be reused across multiple parent processes Collapsed SubCollapse a sub-process to hide internal details and keep the parent diagram readable TransactionUse a Transaction instead when all steps must succeed or all roll back together Error EndErrors thrown inside a sub-process propagate to error boundary events on the sub-process container TaskTasks are atomic; sub-processes decompose work into multiple coordinated steps

Trigger Variants

Sub-Process can be triggered by different mechanisms.

Collapsed Sub-Process

Common Use Cases

Order Fulfillment Phase

Group all fulfillment activities (pick, pack, ship) into a sub-process that can have its own error handling.

Approval Workflow

Encapsulate the multi-step approval flow so boundary events can handle escalation at the approval level.

Repeatable Section

Mark a sub-process as multi-instance to execute the same steps for each item in a collection.

Frequently Asked Questions

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