Activity diagrams

Activity diagrams illustrate the flow of processes in a system. This type of diagram is used to visually document activities within a system, also referred to as a system's procedures or dynamic components. 

The following activity diagram shows the activities involved when a coffee shop customer places an order. The starting point is the top black circle. From there, an order is received. Beneath the Receive Order node is a horizontal black bar referred to as a fork. There are three activities that take place in parallel after the fork—Make Drink, Get Bakery, and Collect Payment. All of those activities take place in parallel. Each of those activities feed into a second black bar, this time referred to as a join, which has multiple activities linked to it. Once all three activities are completed, the order can be completed and ends with the bottom black circle: