Service task

A Service Task represents work performed automatically by a system, without human involvement. In ZenBPM a Service Task does not call the external system itself — when a token reaches the task, the engine creates a job and waits. A job worker (your application) picks the job up, executes the business logic, and completes it, after which the token continues along the outgoing sequence flow.

Rendered as a rounded rectangle with a gear icon in the top-left corner.

Use cases

• Call an external system — charge a credit card through a payment gateway, send a request to a shipping provider, or query a customer record from a CRM.
• Run background processing — generate a PDF invoice, resize an image, or transform a dataset as part of the process.
• Update another system of record — write the process result to an ERP, a database, or a legacy application so downstream systems stay in sync.

Usage in BPMN

To make a Service Task executable, define the job type in a zenbpm:taskDefinition extension element. Optionally, control the data that flows into and out of the task with a zenbpm:ioMapping.

Extension element	Attribute	Required	Description
zenbpm:taskDefinition	type	yes	The job type. The engine creates a job of this type when the task is activated; workers subscribe to this type to receive the job.
zenbpm:ioMapping → zenbpm:input	source, target	no	Maps process variables into the task's local scope, visible to the job worker. See Variables.
zenbpm:ioMapping → zenbpm:output	source, target	no	Maps the job's result variables back to the process scope. See Variables.

Execution flow:

1. A token arrives at the Service Task and the engine creates a job with the configured type, carrying the task's variables.
2. A worker activates the job via the REST or gRPC API (or an internal task handler registered on the engine), performs the work, and completes or fails it.
3. On completion, output mappings are applied and the token moves on. Without output mappings, no variables returned by the worker are propagated to the process scope — define an output mapping for every value you want to keep.
4. On failure, an incident is created; the failure can be handled with an error boundary event.

Related documentation

• Jobs — how jobs are created, distributed, and completed over the REST and gRPC APIs.
• Variables — variable scoping and output mapping propagation rules for activities.

XML example

A Service Task that creates a job of type charge-card. The input mapping passes the order total to the worker as amount; the output mapping stores the worker's transactionId result in the process variable paymentTransactionId.

<bpmn:serviceTask id="Activity_ChargeCard" name="Charge credit card">
  <bpmn:extensionElements>
    <zenbpm:taskDefinition type="charge-card" />
    <zenbpm:ioMapping>
      <zenbpm:input source="=order.totalAmount" target="amount" />
      <zenbpm:output source="=transactionId" target="paymentTransactionId" />
    </zenbpm:ioMapping>
  </bpmn:extensionElements>
  <bpmn:incoming>Flow_In</bpmn:incoming>
  <bpmn:outgoing>Flow_Out</bpmn:outgoing>
</bpmn:serviceTask>