What are Use Cases?

TL;DR — Use cases in 30 seconds

A use case is a description of how a user (called an “actor”) interacts with a system to achieve a specific goal. Use cases capture functional requirements as sequences of steps showing the user-system interaction, including main flow, alternate flows, and exception handling. Standard structure: actor → preconditions → main flow (numbered steps) → alternate flows → postconditions → business rules. Notation: UML use case diagrams (ovals connected to stick figures via lines) plus written use case specifications. Use case vs user story: use cases are detailed and complete (full interaction flow), while user stories are short and focused on user value (“As a user, I want X so that Y”). Most modern teams use both — user stories for backlog grooming, use cases for detailed requirements analysis on complex features. Tools: Visual Paradigm, Lucidchart, draw.io, Enterprise Architect. Common applications: requirements engineering, system design, test case derivation, stakeholder communication.

Definition of Use Cases

Use cases are structured descriptions of interactions between a user or external system (known as an actor) and an information system to achieve a specific goal. Use cases depict how the system should respond to external stimuli, enabling an understanding of the system’s functionality from the user’s perspective. They are a key element in the systems analysis and design process, helping to understand user requirements and facilitating communication between the development team and stakeholders.

Use cases were formalized in the 1990s by Ivar Jacobson and have since become a foundational component of software development methodology. They bridge the gap between business requirements and technical implementation by describing desired system behavior in a format that is understandable to all parties involved. Unlike purely technical specifications, use cases employ natural language that can be understood by both domain experts and developers.

How Use Cases Work

Use cases describe the flow of interaction between an actor and the system in a chronological sequence of steps. The process begins with a triggering event that initiates the use case and ends with the achievement of a defined goal or the occurrence of an alternative outcome.

Each use case defines a main flow (also called the happy path) that describes the ideal interaction sequence, as well as alternative flows that handle variations and exceptions. The main flow describes the step sequence when everything works as expected. Alternative flows address situations where the user makes different decisions or the system must respond to unexpected conditions. Exception flows describe how the system handles errors and invalid inputs.

This structured description enables developers to consider all relevant scenarios and ensure that the system responds appropriately in every situation. Use cases serve as a contract between stakeholders and the development team, defining what the system should do without prescribing how it should be implemented.

Key Elements of Use Cases

Actors

Actors are users or external systems that interact with the system. They are classified by their role rather than by specific individuals. Primary actors initiate the interaction to achieve a goal, while secondary actors are called upon by the system to support the use case. Actors can include human users, external systems, hardware devices, or time-triggered processes.

Scenarios

Scenarios describe the sequence of steps that lead to the actor’s goal. Each step describes either an action by the actor or a response by the system. A well-written scenario is concrete enough to clearly communicate the desired behavior but abstract enough not to prescribe the implementation approach.

Goal

The goal defines the result the actor wants to achieve by interacting with the system. Goals can be defined at different levels, from strategic business goals to operational user goals. Alistair Cockburn’s goal levels framework distinguishes between summary-level, user-goal-level, and subfunction-level use cases, helping teams write use cases at the appropriate level of abstraction.

Preconditions and Postconditions

Preconditions describe the state of the system that must be satisfied before the use case can be executed. Postconditions describe the guaranteed state of the system after successful execution. These conditions help define system boundaries and facilitate the integration of different use cases into a coherent system specification.

Variants and Extensions

Variants describe alternative paths that may occur during use case execution. Extensions are optional flows that augment the main flow with additional functionality. The systematic capture of all variants is critical for the completeness of requirements elicitation and ensures no edge cases are overlooked.

Use Case Diagrams

Use case diagrams are graphical representations of use cases that show the relationships between actors and the system. They are created in the Unified Modeling Language (UML) and help visualize the functionality of the system and the communication between different actors.

Elements of a Use Case Diagram

A use case diagram consists of actors represented as stick figures, use cases represented as ellipses within a system boundary, and relationships between actors and use cases shown as lines. Additionally, relationships between use cases such as include (one use case contains another) and extend (one use case optionally extends another) can be represented. Generalization relationships between actors indicate inheritance of roles.

Practical Usage

Use case diagrams serve as an overview of system functionality and are particularly useful for stakeholder presentations and initial project planning. They show at a glance which functions the system provides and who uses them without diving into the details of individual interactions. However, diagrams alone are insufficient and must be accompanied by detailed textual use case descriptions.

The Process of Creating Use Cases

Identifying Actors and Goals

The use case creation process begins with identifying all actors and their goals. This is accomplished through stakeholder interviews, analysis of existing business processes, and observation of current workflows. Each identified actor is documented with their specific goals and the context in which they interact with the system.

Defining Interaction Scenarios

For each identified goal, interaction scenarios are defined that describe the steps to achieve the goal. It is important that use cases are understandable and precise, so they are often accompanied by use case diagrams that visualize the interactions between actors and the system. Each scenario should focus on a single complete interaction rather than combining multiple goals.

Review and Verification

Once created, use cases are reviewed and verified to ensure they accurately reflect actual requirements. Review sessions with stakeholders, domain experts, and developers help identify gaps, inconsistencies, and ambiguities. Use cases should be traceable to business requirements and testable through acceptance criteria.

Benefits of Use Cases

Use cases offer numerous benefits in software development. They improve communication between technical and non-technical stakeholders through the use of a common, understandable language. They help identify requirements gaps and inconsistencies early in the project lifecycle. Use cases form the basis for test planning since test cases can be derived from each use case scenario. They support project planning and effort estimation by clearly defining the scope of system functionality.

Furthermore, use cases promote a shared understanding of the system among all project participants and serve as an authoritative reference throughout the development phase. They are also valuable in regulated industries where they serve as part of requirements documentation for compliance purposes. Use cases facilitate scope management by providing a clear enumeration of system functionality that stakeholders have agreed upon.

Challenges of Creating Use Cases

Level of Detail

One of the greatest challenges is finding the right level of detail. Use cases should be detailed enough to be useful but not so complicated that they become difficult to understand. Overly detailed use cases can constrain implementation, while overly abstract use cases fail to provide sufficient guidance for developers.

Avoiding Implementation Details

It is important to avoid describing user interfaces or business rules that should be included in other parts of the documentation. Use cases should describe the what, not the how of implementation. Mixing interface design with behavioral requirements reduces the longevity and flexibility of use case documentation.

Consistency and Completeness

Ensuring that use cases are consistent with the actual needs of users and stakeholders and cover all relevant scenarios requires a systematic approach and regular reviews. Cross-referencing between use cases helps identify dependencies and potential conflicts.

Managing Complexity

In large systems, the number of use cases can quickly become overwhelming. Clear structuring and hierarchization of use cases is necessary to maintain clarity. Organizing use cases by business domain or actor group helps manage complexity.

Best Practices in Creating Use Cases

To effectively create use cases, it is worthwhile to involve stakeholders in the development process, regularly review and update use cases, and use standard formats and tools to document them. Use cases should be understandable to all team members and stakeholders to facilitate communication and understanding of project requirements.

It is advisable to build use cases around user goals rather than system functions, use consistent structure and terminology, and link use cases with user stories and acceptance criteria. Using templates and checklists helps ensure the quality and consistency of use cases. Teams should also consider maintaining a glossary of terms to ensure consistent language across all use cases.

Tools for Use Cases

Various tools are available for creating and managing use cases. Enterprise Architect, Visual Paradigm, and StarUML support the creation of UML diagrams and textual use case descriptions. Confluence and Notion are suitable for collaborative documentation, while Jira and Azure DevOps enable linking use cases with development tasks and tracking their implementation status.

ARDURA Consulting and Requirements Engineering

ARDURA Consulting helps organizations acquire qualified business analysts and requirements engineers with deep experience in creating and managing use cases. With a network of over 500 senior IT specialists, ARDURA Consulting can provide experts who structure the requirements elicitation process and improve communication between business and technical teams.

Summary

Use cases are a proven and powerful tool in systems analysis and design that bridges the gap between business requirements and technical implementation. Through structured descriptions of user interactions, use cases help define, communicate, and verify requirements. The combination of textual use case descriptions and visual UML diagrams provides different stakeholders with the appropriate access to system requirements. Despite challenges related to level of detail and consistency, use cases remain an indispensable instrument for successful software development. By adhering to best practices, involving stakeholders throughout the process, and using appropriate tools, organizations can leverage use cases to build systems that truly meet user needs and deliver business value.