Use cases are written scenarios used to test and present the system’s capabilities and form an important part of your high-level design. Though you implement use case scenarios toward the end of the project, formulate them early in the project once you have established your requirements.
When available, use cases can provide valuable insight into how the system is to be tested. Use cases are beneficial in identifying how you need to design the user interface from a navigational perspective. When designing use cases, compare them to your requirements to get a thorough view of their completeness and how you are to interpret the test results.
Use cases provide a method for organizing your requirements. Instead of a bulleted list of requirements, you organize them in a way that tells a story of how someone can use the system. This provides for greater completeness and consistency, and also gives you a better understanding of the importance of a requirement from a user perspective.
Use cases help to identify and clarify the functional requirements of the portal. Use cases capture all the different ways a portal would be used, including the set of interactions between the user and the portal as well as the services, tasks, and functions the portal is required to perform.
A use case defines a goal-oriented set of interactions between external actors and the portal system. (Actors are parties outside the system that interact with the system, and can be a class of users, roles users can play, or other systems.)
Use case steps are written in an easy-to-understand structured narrative using the vocabulary of the domain.
Use case scenarios are an instance of a use case, representing a single path through the use case. Thus, there may be a scenario for the main flow through the use case and other scenarios for each possible variation of flow through the use case (for example, representing each option).
When developing use cases for your portal, keep the following elements in mind:
Priority. Describes the priority, or ranking of the use case. For example, this could range from high to medium to low.
Context of use. Describes the setting or environment in which the use case occurs.
Scope. Describes the conditions and limitations of the use case.
Primary user. Describes what kind of user this applies to, for example, an end user or an administrator.
Special requirements. Describes any other conditions that apply.
Stakeholders. Describes the people who have a vested interest in how a product decision is made or carried out.
Precondition. Describes the prerequisites that must be met for the use case to occur.
Minimal guarantees. Describes the minimum that must occur if the use case is not successfully completed.
Success guarantees. Describes what happens if the use case is successfully completed.
Trigger. Describes the particular item in the system that causes the event to occur.
Description. Provides a step-by-step account of the use case, from start to finish.
Table 3–1 describes a use case for a portal user to authenticate with the portal.
Table 3–1 Use Case: Authenticate Portal User