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Lesson 6 Use cases
Objective Define use cases and how they are used in the use case diagram.

Define Use Cases

Use cases define the required features of the system. Without these features, the system cannot be used successfully.

Focus on system goals

Each use case is named using a verb phrase that expresses a goal the system must accomplish, for example, deposit money, withdraw money, adjust account. Although each use case implies a supporting process, again the focus is on the goal, not the process.

Use case notation

Use case icon

Defining requirements

By defining use cases in this manner, the system is defined as a set of requirements rather than a solution. We do not describe how the system must work. We describe what the system must be able to do. The use cases describe only those features visible and meaningful to the actors who use the system. Keeping this in mind will help you avoid functional decomposition, the breaking down of procedures and tasks into smaller and smaller processes until you have described all the internal workings of the system.

Pitfalls of Systems Development

One of the pitfalls of systems development is going over budget, which happens when we don't limit the scope of each task or we make a model too inclusive. The UML provides seven other models for fully describing the behavior of the software solution for the system, so remember that you can save some ork for later. Step through the process of adding use cases to the use case diagram:

Adding Use Cases
In the next lesson, associations and association stereotypes will be discussed.