Use Case: Definition, Structure, and Practical Benefits
A use case describes the externally visible interaction between a user and a system. The focus is not on the technical implementation, but on the observable goal that an actor wants to achieve by using the system. This concept is particularly common in software development – for example, within the framework of UML (Unified Modeling Language). Project teams use use cases to structure requirements early on and create a common basis for development and testing.
What is a Use Case?
A use case (German: Anwendungsfall) models the interaction between an actor and a system with a view to a specific outcome. An actor can be "a person, an organization, or another system." The process begins with a trigger: a specific trigger prompts the actor to interact with the system. The goal of this interaction – i.e., the desired outcome – defines the use case.
In practice, a use case often consists of two artifacts: a diagram as a graphical overview and a specification, which provides a detailed description of the respective use case.
How does a Use Case work?
A classic example is the ATM. The device is not just "a system," but offers several use cases that differ according to the user's goal: checking the account balance, withdrawing money, or depositing money. The interaction with the system changes depending on the desired outcome.
Additionally, use cases can be divided into business use cases and system use cases . "Ordering food" represents a business-level use case, while "ordering food online" represents the system-oriented use case. This distinction helps to structure goals at different levels of abstraction.
Relationships between use cases can be modeled in diagrams:
- Include Relationships: A regularly required function is integrated as a fixed component. Example: When withdrawing money, the PIN query is a recurring necessary component.
- Extension Relationships: Steps that only occur under specific conditions. Example: Printing a receipt when withdrawing cash.
- Specialization/Generalization: Use cases can be generalized or specialized to represent variations. Example: Unlocking a smartphone can be done via PIN or fingerprint.
Benefits of Use Cases
- Early Guidance: If the most important use cases and their goals are defined at the outset, project stakeholders – especially project managers and teams – gain a common understanding.
- Derivability: Functional requirements and test cases can be systematically derived from use cases.
- Market Acceptance: Without a clearly defined goal, it is difficult for customers to recognize the benefit of a system. In the worst case, the system will not be accepted by the market.
Use Case vs. User Story
Use cases and user stories are often confused. In agile contexts – such as in Extreme Programming environments – the term 'use case' can be reduced to such a concise form that it effectively corresponds to a user story. A user story is "essentially a brief description of a use case." The main difference lies in the level of detail: a complete use case includes a diagram, specification, triggers, and relationships; a user story remains intentionally concise.
Conclusion
A use case purposefully models the interaction between an actor and a system. The combination of diagram and specification, the consideration of triggers and outcomes, and the structured modeling via include, extension, and specialization relationships make the concept a reliable tool in requirements analysis. This provides teams with early clarity about the software's purpose and allows them to derive requirements and test cases directly from it.