4.1. 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 serve as a high-level graphical representation of what a system is designed to do. They illustrate how users interact with the system, showing the functionalities that it provides. This is essential for understanding the overall purpose of the system at a glance.

Think of Use Case diagrams like a movie trailer. Just as a trailer gives you a sneak peek of a film's main story and characters without revealing everything, Use Case diagrams provide insights into the main functions of a system, helping stakeholders grasp its purpose quickly.

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

Use Case diagrams include several key components:

• Actors: These are the people or systems that interact with your application, such as users or external systems.
• Use Cases: These are the functionalities that your system offers, detailing what users can achieve through the application.
• System Boundary: This defines the limits of your system, showing where the system ends and where actors begin.
• Relationships: These explain how different use cases relate to one another. For example, 'Include' means a use case is always part of another use case, while 'Extend' means it's conditionally added. 'Generalization' represents a relationship between more specific actors or use cases.

Consider a restaurant menu.

• The Actors are the customers who come in.
• The Use Cases are the dishes on the menu.
• The System Boundary is the kitchen, which contains the process of making the food (your use cases).
• Relationships like 'Include' might represent how an appetizer is always part of a meal deal, while 'Extend' could indicate a special dessert is optionally added if customers choose a certain main course.

Example: In an e-commerce system: ● Actor: Customer ● Use Cases: Register, Login, Search Product, Add to Cart, Checkout, Make Payment Use Case Diagram Sample: ● Customer --> (Search Product) ● Customer --> (Add to Cart) ● Customer --> (Checkout) ● (Customer) -->(Make Payment)

In an e-commerce system, a Customer is the actor who interacts with various use cases, which represent different functionalities of the platform. The examples of use cases such as Register, Login, Search Product, Add to Cart, and Make Payment illustrate the actions a customer can perform. For each interaction depicted in the diagram, arrows indicate the relationship between the actor and the use cases, showcasing user activities within the system's boundary.

Imagine a customer entering a clothing store. Each time they do something – like browsing (Search Product), trying things on (Add to Cart), or going to the checkout – it mirrors the actions represented in the use case diagram. Just as the store is organized to facilitate these customer actions, the e-commerce diagram outlines how users will interact with the system.

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

Business Analysts (BAs) use Use Case diagrams to define what the system should do from the end-user's viewpoint. This perspective is crucial for identifying who the users are (the roles) and understanding their goals when using the system. Additionally, these diagrams help BAs confirm that they have accurately captured the system's functionalities and requirements with key stakeholders, ensuring everyone is on the same page regarding what the system should accomplish.

Consider a teacher gathering requirements for a new school project. They need to understand the students’ roles, like who will be doing research, presenting, or gathering materials. Use Case diagrams are akin to a project outline that helps the teacher ensure that all the necessary components and roles are aligned with the students' educational goals.

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