UseCaseDiagrammen

UseCaseDiagrammen, or use case diagrams, are a graphical tool used in software engineering and requirements analysis to visualize how external actors interact with a system through its functions. They focus on what the system should do from the user's perspective, rather than on internal structure or technical implementation. The diagrams aid communication among stakeholders and help define system scope and user goals.

Core elements include a system boundary (a rectangle labeled with the system name), actors (external roles or other systems, depicted as stick figures or icons) outside the boundary, and use cases (functionalities or services, shown as ovals inside the boundary). Associations (lines) connect actors to the use cases they participate in, illustrating who can perform which functions.

Common relationships in UseCaseDiagrammen are include, extend, and generalization. Include represents a use case that is always executed as part of another; extend denotes optional or conditional behavior that extends a base use case; generalization captures specialization among actors or use cases. These relationships help model reuse and variability without duplicating effort.

Construction typically starts with defining the system boundary, identifying actors and primary use cases, drawing associations, and then refining the diagram with include/extend relationships. Names for use cases are usually action-based and concise, focusing on user goals.

Benefits and limitations: use case diagrams provide a high-level, stakeholder-friendly view of system functionality and scope, supporting requirements elicitation and traceability. They can become oversimplified for complex systems and should be complemented by other UML diagrams for detailed design.

See also: UML, Anwendungsfalldiagramm, Use Case. Example: in an online bookstore, actors might include Kunde (customer) and Kreditkartendienst, with use cases such as Suche Buch, Bestellung aufgeben, Zahlung abwickeln.