Here is an analogy:
- The flow sequence is your agenda for a day: Start at home, Go to work, Go buy groceries from a supermarket, Go home, Go to a gym, Go home
- Process groups are the operations / activities. In this case Home, Work, Supermarket, Gym. There are many supermarkets and gyms (process implementations), any of which can be used, but only one home and workplace.
- Transport system is the road network and public transit / taxi service which enable you to get to those processes.