Define flow objects

In BPMN, flow objects are the fundamental building blocks that describe the behavior of a business process. They represent the work that is done, the path the work takes, and the events that occur. There are three main types of flow objects:

1. Events: These represent something that happens during the course of a business process. Events can trigger a process, occur during a process, or mark the end of a process. They are depicted as circles. Examples include a "Start Event" (a thin circle), an "Intermediate Event" (a double circle), and an "End Event" (a thick circle).

2. Activities: These represent the work that is performed in a process. Activities can be tasks (a single unit of work) or subprocesses (a complex process that can be expanded). They are depicted as rounded rectangles.

3. Gateways: These control the flow or divergence and convergence of sequence flows. They determine whether a process splits into multiple paths, merges multiple paths into one, or makes a decision. They are depicted as diamonds.