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Modeling Processes, Sub-Processes, and Tasks in BPMN business process diagrams
An activity is work that an organization performs. There are three types of activities: Process, Sub-Process, and Task. You can model these activities on BPMN diagrams.
Process, Sub-Process, and Task are all graphically depicted using the same symbol. The use of different nouns reflects the hierarchical relationships between them. However, the Transaction process is represented differently.
A Process is a network of “doing things”.
A Sub-Process is a decomposition of a Process.
A Task is a decomposition of a Process that itself does not have any further decomposition. In other words, the Task is the lowest-level process.
See also
BPMN Process definitions
Drawing processes, subprocesses, and tasks on BPMN diagrams
BPMN