or cannot be broken down to a further level of business process detail. It is referred to as an atomic activity. A task is the lowest level activity illustrated on a process diagram. A set of tasks may represent a high-level procedure. Sub-process Used to hide or reveal additional levels of business process detail. When collapsed, a sub-process is indicated by a plus sign against the bottom line of the rectangle; when expanded, the rounded rectangle expands to show all flow objects, connecting objects, and artifacts. A sub-process is referred to as a compound activity. Has its own self-contained start and end events; sequence flows from the parent process must not cross the boundary. Transaction A form of sub-process in which all contained activities must be treated as a whole; i.e., they must all be completed to meet an objective, and if any one of them fails, they must all be compensated (undone). Transactions are differentiated from expanded sub-processes by being surrounded by a double border. Call Activity A point in the process where a global process or a global Task is reused. A call activity is differentiated from other activity types by a bolded border around the activity area. Gateway A gateway is represented with a diamond shape and determines forking and merging of paths, depending on the conditions expressed. Exclusive Used to create alternative flows in a process. Because only one of the paths can be taken, it is called exclusive. Event Based The condition determining the path of a process is based on an evaluated event. Parallel Used to create parallel paths without evaluating any conditions. Inclusive Used to create alternative flows where all paths are evaluated. Exclusive Event Based An event is being evaluated to determine which of mutually exclusive paths will be taken. Complex Used to model complex synchronization behavior. Parallel Event Based Two parallel processes are started based on an event, but there is no evaluation of the event. Connections Flow objects are connected to each other using Connecting objects, which are of three types: sequences, messages, and associations. Sequence Flow A Sequence Flow is represented with a solid line and arrowhead, and shows in which order the activities are performed. The sequence flow may also have a symbol at its start, a small diamond indicates one of a number of conditional flows from an activity, while a diagonal slash indicates the default flow