Figure 8-2. Both activities as one unique use case.
After presenting the use case model, it is important to provide a description of what the use case is supposed to do. A use case description helps people involved in the process of the software development to understand the functionalities encapsulated in the use case and to facilitate the discussion about the validity of the use case.
Let us consider the Start Simulation use case and provide a potential description for it. One possible brief description of this use case can be the following:
This use case describes how a user can perform a crop simulation process. The data entered by the user define the initial conditions for plant and soil. After the calculations are terminated, the results are displayed in the window.
The brief description is important and if the use case is simple enough, all it can be provided with is the brief description. When the use case is complex, additional information is required. A more detailed description of the use case can be given in the form of an outline. The outline shows the simple steps of the use case using short sentences and presented in a timely manner. The focus at this point is on the clarification of the basic flow of the events. The basic flow (or the main flow) does represent a description of the normal and expected path of the execution of the use case. Some authors refer to the basic flow of events as the happy scenario, where everything goes well and nothing goes wrong.
Later, the focus will shift into presenting the most significant alternatives and exceptions, thus shedding more light on the complexity of the use case. An alternative flow of events represents a possible execution route from the starting point to the end of the use case that is different from the basic flow. An alternative flow represents one of the scenarios where something is not executed as predicted. Thus, most of the alternative flows represent the errors that may occur during the execution of the use case. The basic flow represents the successful route from the beginning to the end of the use case. The alternative flows show all the detours (unsuccessful executions) that may occur during the execution of the use case.
An outline for the use case Start Simulation can be the one presented in the next section.
2.2 Basic flow
1. The use case starts when the user clicks on the Start Simulation button.
2. Initialize plant, soil, and weather.
3. Loop through the weather data:
a. Calculate rate for soil and plant.
b. Integrate soil and plant.
4. End of the weather loop.
5. The use case ends.
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