UseCaseRequirements

Use Case-based Requirements

Introduction to Use Cases

• Overview of documenting requirements using use cases.

• Topics covered include:

  • Symbols in use case diagrams

  • Relationships between symbols

  • Textual description of use cases

Object-Oriented Programming Context

• Use cases facilitate better documentation and discovery of classes needed in programming environments (e.g., Java, C++).

• Documentation aids in design, testing, and user manual creation.

Introduction to UML (Unified Modeling Language)

• UML provides a standardized way to visualize system design.

  • Types of UML diagrams include:

    • Use case diagrams for requirements

    • State diagrams for analysis

    • Class and sequence diagrams for design

• Proficiency in UML is essential for effective collaboration in software development.

Scenario-based Requirements Elicitation

Scenarios

• A scenario is a specific sequence of actions depicting behavior.

• Illustrates how users interact with a system (e.g., Monopoly game example).

Scenario-based Approach

• Used to gather and validate requirements through descriptive storytelling.

• A complete set of scenarios represents all functionalities of the system.

Elements of a Use Case

Definition

• Use case: A specification of action sequences involving system interactions with outside actors.

• Scenarios are tied to common user goals, presenting measurable results for actors.

Use Cases Made Up of Scenarios

• Multiple scenarios can be included in one use case demonstrating various pathways (successful and error conditions).

UML Symbols

• Use case: represented by an oval.

• Actors: represented as stick figures, indicating entities that interact with the system.

Identifying Actors

• To identify actors, ask:

  • Who uses/install/maintain/shut down the system?

  • What information is exchanged?

Identifying Use Cases

• Identify expected measurable outcomes actors seek from the system.

Use Case Diagrams and Relationships

Diagram Construction

• Visual representation showing relationships among actors and use cases using UML conventions.

Relationships

1. Communication: Default relationship, indicating interaction initiation.

2. Include relationship: When one use case incorporates the functionality of another.

3. Extend relationship: Provides variation or exception flows.

Use Case Flow-of-Events

Importance

• Provides detailed procedure of a use case, focusing on what the system should do, detailed in a structured template.

Flow-of-Events Template Structure:

• Preconditions: What must occur before use.

• Main Flow: Steps involved in the use case performance.

• Sub-flows: Breakdown of main flow for clarity.

• Alternative Flows: Define reactions to errors or unusual conditions.

Misuse Cases

• Misuse cases consider the perspective of hostile actors threatening system security.

• Essential for planning security measures and identifying vulnerabilities.

Use Cases in Software Requirements Specification (SRS)

• Use cases can replace traditional functional requirements in an SRS, aiding clarity and stakeholder understanding.

• SRS includes traceability mapping for comprehensive requirements coverage.

Nonfunctional Requirements

• Emphasize system performance, usability, and user interface effectiveness.

Summary of Practical Tips

• Identify all system actors.

• Gather comprehensive actor requested functionalities.

• Reuse common functionalities through include relations.

• Avoid complexity by minimizing use of extend relationships.

• Use diagrams and flow descriptions for clearer requirements comprehension.