Use Case

Represent required externally observable system behavior as an actor pursuing a goal across a system boundary through a main interaction flow plus declared alternatives, exceptions, preconditions, and outcomes.

Version

v2 · 2026-09-06 · History

Domain-specific #

3047

Origin domain

engineering

Subdomain

requirements engineering

Aliases

Usage case

Core Idea

A use case is a requirements representation of how a subject system provides behavior of value to an external actor. UML defines the subject as the system under consideration, actors as external roles or systems that interact with it, and use cases as specifications of required behavior according to actor needs. The identity therefore couples an external role, a goal, a system boundary, and a behavior contract; a mere example of how a product might be used is too weak.

Scope of Application

The construct is literal in software and systems requirements work where externally initiated, goal-directed behavior must be represented and validated.

• Requirements elicitation. Turning stakeholder goals and interactions into reviewable behavior descriptions.
• System scoping. Locating actors and responsibilities across a declared boundary.
• Functional decomposition. Organizing related required behaviors without prematurely choosing components.
• Acceptance planning. Deriving scenarios and observable outcomes for validation.
• Architecture dialogue. Exposing cross-system interactions and service responsibilities to designers.
• Change impact. Tracing a modified actor goal or flow to requirements, tests, and affected interfaces.

Clarity

Give the use case a goal-oriented verb phrase, name the subject and primary actor, state stakeholder interest, preconditions, trigger, main success flow, alternatives, exceptions, and postconditions. Number steps so extensions have explicit attachment points. Write interactions in observable terms and identify which side acts. Do not encode a screen sequence as though it were the requirement unless the interface itself is constrained. Separate reusable subordinate behavior from optional extensions and use UML include/extend relations only with their formal direction and semantics.

Manages Complexity

A use case compresses many stakeholder statements into a bounded interaction contract. The actor and goal select relevant behavior; the system boundary assigns responsibility; the main flow shows the ordinary path; and alternate flows keep exception detail attached rather than scattering it across prose. This makes omissions visible: a goal without a success outcome, an actor without a permitted interaction, or an exception without a recovery state can be challenged directly.

Abstract Reasoning

1. Choose the system-of-interest and draw its responsibility boundary.
2. Identify external actor roles and the stakeholder goal each seeks.
3. Name the trigger, preconditions, and minimum success guarantee.
4. Write the main actor-subject interaction flow at an observable level.
5. Attach alternate and exception flows to explicit conditions or steps.
6. State postconditions for success, failure, and any partial result.
7. Review the case for hidden design commitments and missing quality constraints.
8. Trace approved behavior to requirements, tests, interfaces, and validation evidence.

Knowledge Transfer

The strict parent is Representation: a use case maps selected aspects of stakeholder goals and system behavior into a textual or model-based medium under an interpretation convention. The use-case residual is the actor–subject boundary, goal, interaction flows, and outcome contract. Scenario Planning is related at a surface level but constructs alternative futures rather than required system behavior.

Relationships to Other Abstractions

Current abstraction Use Case Domain-specific

Parents (1) — more general patterns this builds on

• Use Case is a kind of Representation Prime

  Representation is the strict parent because the use-case artifact selectively encodes externally required behavior for stakeholder interpretation and downstream operations.

Hierarchy path (1) — routes to 1 parentless root

• Use Case → Representation → Abstraction

Neighborhood in Abstraction Space

Use Case sits in a sparse region of the domain-specific corpus (92^nd percentile for distinctiveness): few abstractions share its structure, so a faithful description tends to retrieve it precisely.

Family — Unclustered & Miscellaneous (1565 abstractions)

Nearest neighbors

• Sequence Diagram — 0.79
• Specification language — 0.78
• Proxy Pattern — 0.78
• Commander's-Intent Ambiguity — 0.78
• Isolated System — 0.77

Computed from structural-signature embeddings · 2026-09-08