3.1. Purpose

To represent high-level functional interactions between actors (users or systems) and the system. These diagrams help define the scope of the system and its functionality.

Use case diagrams are graphical representations used to show how different users or systems interact with a software system. This definition emphasizes that these diagrams capture the primary objectives or goals that users have when interacting with the system, providing clarity on what the system is supposed to accomplish.

Imagine planning a party. A use case diagram would represent all the roles (like hosts, guests, and caterers) and their interactions (such as RSVP, food ordering, and entertainment) with the party. This helps clarify what needs to happen for the party to be successful.

Key Components: ● Actors: External users or systems interacting with the application ● Use Cases: Functionalities the system provides ● System Boundary: Encapsulates use cases within the system ● Relationships: ○ Include: A use case always includes another (common logic) ○ Extend: A use case optionally extends another (conditional logic) ○ Generalization: Inheritance between actors or use cases

This chunk breaks down the main elements that make up use case diagrams: actors represent users or systems interacting with the software, while use cases illustrate what the software does. The system boundary defines what is included in the software's functionality. Relationships describe how use cases relate to one another, which include 'include' for mandatory actions, 'extend' for possible but not necessary actions, and 'generalization' for commonality between different user roles or cases.

Think of actors as guests at a restaurant (customers, servers, chefs). Each guest (actor) has specific actions they can do, like placing an order or serving food (use cases). The restaurant itself is the boundary that defines these interactions, while the relationships help understand how different actions, like ordering a drink (include), may optionally include adding a dessert (extend), showing the flexibility of options.

BA’s Usage: ● Define system functionality from an end-user perspective ● Identify user roles and their goals ● Validate functional scope with stakeholders

Use case diagrams are useful tools for Business Analysts (BAs) because they help clearly define what the system should do from the perspective of the end users. This allows BAs to pinpoint different user roles within the system and their specific objectives or tasks. Additionally, these diagrams serve as a reference point for discussions with stakeholders to ensure everyone has a shared understanding of the system's functionalities.

Imagine a team working on a new app. The BA uses a use case diagram to illustrate what features the app will include, like messaging and photo sharing. By doing so, team members can see the app through the users' eyes, identifying what is necessary for success and what may require further development, much like a pilot reviewing the flight plan with the crew before takeoff.

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