Lecture 31: Use Case Modelling - Capturing Functional Requirements from a User's Perspective
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Introduction to Use Case Modelling
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Today, we'll discuss Use Case Modelling. Letβs start with a definition: Use Case Modelling captures functional requirements from the user's perspective, focusing on what a system does rather than how it does it.
Why is it important to focus on users and not just the system itself?
Great question! By focusing on user interactions, we ensure that the requirements are relevant and understandable for stakeholders. This user-centric approach helps in validating the requirements effectively.
How does it facilitate communication?
Use Case Modelling serves as a common language between users, clients, and developers, bridging gaps in understanding about system functionality.
So, does it help in designing other models as well?
Absolutely! Use Cases are foundational; they guide the creation of other models like Class and Sequence Diagrams.
In summary, Use Case Modelling captures what the system does through a user-centric lens, promotes better understanding, and drives the creation of additional models.
Key Elements of a Use Case Model
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Now letβs dive into the key elements of a Use Case Model: actors, use cases, the system boundary, and their relationships. Who can tell me what an Actor is?
Isn't it anyone who interacts with the system?
Exactly! An Actor represents any external entity that interacts with the system. They initiate use cases or receive outputs. Can you name some types of actors?
There are primary, supporting, and passive actors?
Spot on! A Primary Actor initiates a use case, while Supporting Actors provide services to the system. Passive Actors receive benefits from the system. Next is the Use Case itself β what do we know about it?
Use Cases describe sequences of actions yielding observable results.
You got it! And they should be goal-oriented. Now, what about the System Boundary?
It's the rectangle that defines the scope of the system, right?
Correct! Now letβs recap: we identified Actors, Use Cases, the System Boundary, and their roles in connecting the system with its users.
Use Case Diagrams and Specifications
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Letβs talk about Use Case Diagrams. What do they provide?
A graphical overview of actors, use cases, and their relationships?
Exactly! Use Case Diagrams summarize system functionality and illustrate interactions visually. Why are they useful?
They make it easier to understand complex systems at a glance.
Right! Now, moving on to Use Case Specifications, who can explain their importance?
They detail the sequence of events and conditions, providing clarity.
Well said! Essential elements here include Use Case Name, Actors, Preconditions, and Normal Flow. Letβs think of an example for 'Place Order.'
Like having to be logged in and having items in the cart before placing an order?
Precisely! These details ensure a complete and meaningful description. Let's summarize: Use Case Diagrams provide a visual overview, while Specifications provide detailed narratives.
Introduction & Overview
Read summaries of the section's main ideas at different levels of detail.
Quick Overview
Standard
In this section, Use Case Modelling is presented as a powerful tool for articulating functional requirements by focusing on external actors' interactions with the system. It highlights essential components like Actors, Use Cases, and system boundaries, thereby providing a framework for visualizing system functionality and enhancing stakeholder communication.
Detailed
Detailed Overview of Use Case Modelling
Introduction
Use Case Modelling plays a pivotal role in object-oriented analysis, designed to capture functional requirements from an external user's viewpoint. By defining what a system does and illustrating how users interact with it, this technique fosters clarity and facilitates dialogue between stakeholders, ensuring requirements are easily understandable and verifiable.
Key Elements of a Use Case Model
- Actor: Represents an external entity that interacts with the system. Actors can be human users, other systems, or devices, and are categorized as primary, supporting, passive, or time-based.
- Use Case: Defines a sequence of actions yielding a result of value, described from the actorβs perspective. Use cases are goal-oriented and use a naming convention of strong verbs followed by noun phrases.
- System Boundary: Illustrated by a rectangle, it encases all use cases, delineating what is included within the system.
- Relationships: Associations illustrate interactions between actors and use cases, represented by lines indicating communication.
Use Case Diagrams
A graphical snapshot summarizing actors, use cases, and their relationships within the defined system boundary, contributing to an overarching understanding of the systemβs functional scope.
Use Case Specifications
These are detailed textual descriptions that elaborate on the use case, presenting the normal and alternative flows of events, preconditions, and postconditions, enhancing the clarity of functional requirements. Each use case specification serves as a guide to understand the system dynamics and user interactions better.
Key Concepts
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Use Case Modelling: A technique to capture functional requirements from the user's viewpoint.
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Actors: External entities interacting with the system.
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Use Case: Describes how actors achieve goals with the system.
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System Boundary: Defines the scope of the system under consideration.
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Use Case Diagram: Visual representation of actors and their interactions with use cases.
Examples & Applications
An online shopping system where 'Customer' is an actor initiating the use case 'Place Order'.
In a library management system, 'Librarian' as an actor can manage books and patrons through various use cases.
Memory Aids
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Rhymes
Actors act, Use Cases chase, within the boundaryβs embrace.
Stories
Imagine a library where every visitor (actor) uses a catalog (use case) to find a book β the libraryβs walls (system boundary) keep them focused on stories without distractions.
Memory Tools
A.U.S. = Actor, Use Case, System Boundary.
Acronyms
UML = Understanding Models Legibly.
Flash Cards
Glossary
- Actor
An external entity that interacts with the system, initiating use cases or receiving value from the system.
- Use Case
A sequence of actions yielding an observable result of value to a particular actor, describing system functionality.
- System Boundary
A rectangle representing the scope of the system, with use cases enclosed and actors outside.
- Use Case Diagram
A graphical representation showing actors, use cases, and their relationships within the system boundary.
- Use Case Specification
A detailed textual description of a use case, outlining the sequence of events, conditions, and flows.
Reference links
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