Part of the basic flow in a use case may be to iterate through a number of its steps. If so, then the problem is to define the iteration using natural language without the resort to computer constructs so that the text remains understandable to not technical people like users. This requires the use of a sentence, usually at the end of the loop, which defines the iteration in terms of where it starts, where it ends, and the condition for the exit from the loop. This can be done in a number of ways, the simplest generally being the most effective because they are the easiest to understand.

Use the following guidelines:

	Number each sentence in the flow and refer to them in the iteration for the start and end points.
	The condition for exit from the loop is often the occurrence of the next incoming event, if it is an external event that causes the exit from the loop. If this is the case then the condition may not need to be specified in the iteration sentence.
	If, however, the condition that causes the exit from the loop is internally calculated, then a statement of that condition will need to be included in the iteration sentence.

	Any simple exception to the basic flow is normally specified in an alternate flow which is a separate paragraph from the basic flow.
	If the iteration and the selections are multiple and nested, then the best approach is not to try to describe them using words. Instead, define each flow as a separate sub-flow (see next chapter) and use an activity diagram which refers to each flow.