An activity is work that a company performs. There are three types of activities: Process, Sub-Process, and Task. Each are graphically depicted using the same symbol. The use of different nouns merely reflects the hierarchical relationships between them.
▪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.
A process is a rounded rectangle represented on the top-level BPMN Business Process diagram. You can specify the inner details of a process by creating or attaching another Business Process diagram to it. The subdiagram is considered a “child diagram”. A process that has a child diagram is indicated by + (plus sign) in its body.
Graphically showing the details of a process with another Business Process diagram is considered “decomposing” the process. You can continue to decompose a process without any restriction: creating a child diagram for a process, and child diagrams for the processes on the first child diagram, and so on. Processes that you draw on child diagrams are considered subprocesses. The lowest-level process, which you do not decompose further, is considered a task.
As the figure below shows, it is easy to pick out a task from a subprocess on a diagram: a task does not have + (since it is not decomposed).
