L04 Use Case Description

Summary

This transcript discusses the fundamentals of use case modeling and writing, emphasizing the importance of identifying all possible scenarios within a use case to ensure the system can handle them. It outlines the main components of a use case description, including the use case name, ID, description, primary and secondary actors, preconditions, postconditions, main flow, and alternate flows. The guidelines for writing use case descriptions are provided, highlighting the need to clearly show the actor's control and avoid imposing constraints on the user interface. Examples and templates are given to illustrate how to write detailed and effective use case descriptions.

Takeaways

• 📝 Use case descriptions are essential for detailing the steps and variations in achieving user goals within a system.
• 🔍 Each use case has internal complexity, which includes various scenarios and possible sequences of actions to reach the desired outcome.
• 🏢 Use case models alone cannot convey the full details of system functionality; thus, use case descriptions complement them by explaining what occurs within each use case.
• 📌 A use case description typically includes the use case name, ID, a high-level overview, and outcomes, as well as details on primary and secondary actors.
• 🔗 Precondition and postconditions are crucial parts of a use case description, outlining what must happen before and after the use case execution.
• 🌟 The main flow outlines the normal expected sequence of user actions and system responses that lead to the accomplishment of the use case goal.
• 🛠 Alternate flows detail different scenarios and variations of the main flow, providing a comprehensive view of how the system handles different situations.
• 📈 Use case descriptions should be based on information gathered during the requirements phase and should not impose constraints on the user interface design.
• 🎯 When writing use case descriptions, always start with the actor to clearly show who is in control, and avoid specifying UI elements too early in the process.
• 🔄 Use case descriptions can include extension points and included use cases, showing how they relate to base cases and providing a structured approach to complex functionalities.

Q & A

What are the main components of a use case?

The main components of a use case include the use case name, a unique use case ID, a high-level description of the sequence of actions, the primary and secondary actors, preconditions, postconditions, the main flow, and alternate flows.

What is the purpose of a use case description?

A use case description serves to detail the internal complexity of a use case, outlining the sequence of steps required to execute the business process and achieve the user's goal. It also identifies all possible scenarios that may arise when executing the use case.

How does a use case model help in system's functional requirements specification?

A use case model is instrumental in modeling the system's functional requirements by specifying user goals. It provides a visual representation of how the system should interact with users to fulfill their needs.

What are the differences between primary and secondary actors in a use case?

The primary actor is the one who triggers or initiates the use case, also known as the initiator. The secondary actor is the one that interacts with the use case after it has been triggered, sometimes referred to as a participator.

What are preconditions in a use case?

Preconditions are the activities that must have taken place or conditions that must be true before the use case can be started. They set the stage for the use case to occur.

What are postconditions in a use case?

Postconditions describe the state of the system at the conclusion of the use case execution, outlining the changes in system state or data as a result of the use case being executed.

How should the main flow of a use case be written?

The main flow should list the user's actions and system responses that take place during the execution of the use case under normal expected conditions. It should clearly show the sequence of actions and responses that lead to the accomplishment of the goal stated in the use case name.

What are alternate flows in a use case and how should they be represented?

Alternate flows represent other legitimate usage scenarios that can occur within the use case. Each alternate flow should be preceded with a scenario name and should list the user's actions and system responses for that particular scenario.

What are some guidelines for writing use case descriptions?

When writing use case descriptions, always start with the actor to show who is in control, avoid imposing constraints on the user interface, and clearly indicate how the user inputs data or makes selections. The descriptions should be concise, clear, and focused on the interactions between the actor and the system.

How can you indicate repeated steps in a use case description?

To indicate repeated steps, you can use a construct like 'repeat step X to Y' to denote the repetition of a series of steps. This should be used when a specific number of repetitions is known or when the repetition is conditional.

How do you describe an extended use case or an included use case in a use case description?

An extended use case is described by stating it as an extension of the base use case and detailing the specific requirements added. An included use case is described by indicating the point in the main flow where the included use case is triggered and detailing the steps involved in the included use case.