Use Cases

Definition and Purpose

What Is a Use Case?

Use case: textual or diagrammatic description of system-user interaction. Purpose: capture functional requirements from user perspective. Originated in UML and requirements engineering. Focus: goal-oriented scenarios illustrating system behavior under certain conditions.

Historical Context

Introduced by Ivar Jacobson in 1986. Adopted in UML 1.0 (1997). Became a standard for capturing functional requirements and bridging communication gaps among stakeholders.

Purpose in Requirements Engineering

Clarifies system boundaries, user goals, preconditions, and expected outcomes. Facilitates validation of requirements. Supports traceability from requirements to design and testing.

"Use cases provide a bridge between users’ needs and system design, ensuring alignment and clarity." -- Ivar Jacobson

Core Components

Actors

Entities interacting with system: human users, external systems, devices. Role-based abstraction. Primary vs secondary actors distinction.

Use Case Name and Identifier

Unique descriptive label. Facilitates reference and organization. Often includes numbering scheme.

Preconditions

Conditions that must hold before execution. Defines valid system and actor state for use case initiation.

Basic Flow (Main Success Scenario)

Stepwise description of normal interaction leading to goal achievement. Core path without errors or exceptions.

Alternative Flows

Variations and exceptions. Capture error handling, branching conditions, and alternate user choices.

Postconditions

System state after successful or failed completion. Validates outcome and side effects.

Types of Use Cases

Brief Use Cases

High-level summaries. Focus on goals and actors without detailed steps. Useful for early requirements elicitation.

Casual Use Cases

Moderate detail with main success scenario plus few alternatives. Suitable for iterative refinement.

Fully Dressed Use Cases

Comprehensive descriptions including all flows, conditions, and extensions. Employed in complex systems and formal documentation.

Notation and Representation

Textual Format

Template-driven, structured prose with sections: name, actors, preconditions, flows, postconditions.

UML Use Case Diagrams

Visual abstraction showing actors, use cases, and relationships (include, extend, generalization). Focus on interaction scope.

Relationships in Diagrams

Include: mandatory sub-use case invocation. Extend: optional or conditional behavior. Generalization: inheritance among use cases or actors.

Writing Effective Use Cases

Clarity and Conciseness

Use simple, unambiguous language. Avoid technical jargon unless necessary. Focus on user goals and system responses.

Consistency

Uniform format and terminology. Maintain naming conventions for actors and use cases. Use glossary if needed.

Completeness

Cover normal and alternative flows. Specify preconditions and postconditions. Ensure all user interactions are represented.

Testability

Describe steps to allow validation via test cases. Define measurable success criteria.

Benefits and Limitations

Benefits

Improves stakeholder communication. Captures user-centered requirements. Facilitates validation and verification. Supports design and testing alignment.

Limitations

May omit non-functional requirements. Can be verbose if overly detailed. Requires skilled authorship. Not suitable for all system types (e.g., low-level technical specs).

Relationship with Other Artifacts

Use Cases and User Stories

User stories: agile, lightweight requirements. Use cases: detailed, structured scenarios. Complementary in hybrid processes.

Use Cases and Functional Requirements

Use cases describe functional requirements contextually. Functional requirements specify system capabilities in detail.

Use Cases and Test Cases

Use cases form basis for deriving test cases. Traceability links requirements to verification.

Tools Supporting Use Cases

Requirements Management Tools

Examples: IBM DOORS, Jama Connect. Features: version control, traceability, collaboration.

UML Modeling Software

Examples: Enterprise Architect, Visual Paradigm. Support use case diagrams and textual documentation.

Collaborative Platforms

Examples: Confluence, Jira. Facilitate iterative writing, review, and linking with other artifacts.

Application in Software Development

Requirements Elicitation

Use cases aid stakeholder interviews and workshops. Reveal hidden requirements and user goals.

System Design

Guide architectural decisions and component interactions. Define interfaces and responsibilities.

Testing and Validation

Derive acceptance criteria and test scenarios. Ensure system fulfills user expectations.

Best Practices

Engage Stakeholders Early

Involve users and domain experts to gather accurate use cases. Validate assumptions continuously.

Iterative Refinement

Start with brief use cases, progressively add detail. Adapt to changing requirements.

Maintain Use Case Repository

Organize and version control use cases. Facilitate reuse and consistency across projects.

Examples and Templates

Simple Use Case Example

Use Case: Login to SystemActors: UserPreconditions: User is registeredBasic Flow:1. User enters username and password2. System validates credentials3. System grants accessPostconditions: User is authenticatedAlternative Flows:2a. Invalid credentials -> System displays error

Use Case Template

Common Errors and Pitfalls

Over-Detailing

Excessive steps obscure main goals. Difficult to maintain and review.

Ignoring Alternative Flows

Leads to incomplete requirements and undetected edge cases.

Mixing Functional and Non-Functional Requirements

Use cases unsuitable for performance, security, and usability specifications.

Ambiguous Language

Creates misunderstanding and implementation errors. Avoid vague verbs and pronouns.

References

• Jacobson, I., Christerson, M., Jonsson, P., & Övergaard, G. "Object-Oriented Software Engineering: A Use Case Driven Approach." Addison-Wesley, 1992.
• Cockburn, A. "Writing Effective Use Cases." Addison-Wesley, 2000.
• Rumbaugh, J., Jacobson, I., & Booch, G. "The Unified Modeling Language Reference Manual." Addison-Wesley, 2004.
• Alexander, I., & Beus-Dukic, L. "Discovering Requirements: How to Specify Products and Services." Wiley, 2009.
• Wiegers, K., & Beatty, J. "Software Requirements." Microsoft Press, 2013.