User manual

9. Use Cases
In this chapter we utilize “use cases” to illustrate the functionality of the
Centralized Phonebook Database as seen by the designer. Use cases are a widely used
and useful method to discover and understand functional requirements that indicate what
the system will do. Use cases are also a mechanism to help keep it simple and
understandable for all stakeholders. They are a model for describing the system’s
functionality and environment. In essence, use cases are a way of discovering and
recording functional requirements by writing stories of the use a system to help fulfill
stakeholders’ goals.
There are six parts to a use case:
• Primary Actor. The primary actor is the entity that performs the majority of the
actions that are critical to the use case. Examples of actors are a person, computer
system, or organization.
• Stakeholders and Interest. Stakeholders are the entities that have an interest in
the success of the scenario. This section includes a list of stakeholders and their
interests in the scenario.
• Preconditions. These are the conditions that need to be fulfilled before the
scenario in the use case begins. These conditions are not tested in the scenario,
instead, they are assumed to be true when the scenario starts.
• Success Guarantee (post-condition). This is the result of a successfully
completed scenario. The guarantee should meet all the needs of the stakeholders.
• Main Success Scenario. The list of steps that describes the typical success path
that satisfies the interest of the stakeholders.
• Extension (or Alternative Flow). Indicates other scenarios or branches for both
success and failure from the main success scenario.
We created three use cases for the CPD. The three use cases are: Phonebook Upload
to Server, Phonebook Access via Voice Mail, and Phonebook Access via Webpage
Interface. We chose these three scenarios because they are the three main functionalities
of the CPD system that involve the cell phone user. All scenarios have the cell phone
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