Use Case Specification

Instructions

Create or update use case specification documents for $ARGUMENTS in docs/use_cases/. Each use case describes a complete interaction between an actor and the system to achieve a goal.

File naming (do this exactly)

One file per use case, written to docs/use_cases/UC-XXX-<kebab-case-name>.md where:

• UC-XXX is the use case's three-digit ID (e.g. UC-001).
• <kebab-case-name> is the use case name taken verbatim from the use case diagram (docs/use_cases.puml), lowercased with spaces replaced by hyphens. Do not paraphrase, expand, or reorder the words.

Scope: one or many use cases

• If the task names a single use case (e.g. "write UC-001 Place Order"), produce only that one file. Do not create specs for other use cases in the diagram.
• If the task asks for "all use cases" or names several, produce one file per use case:
  • UC-XXX IDs come from the diagram and never repeat.
  • BR-XXX business-rule IDs are unique within their own file only and restart at BR-001 in every file — the use case is the namespace. When referring to a rule of another use case, qualify it with the use case id (e.g. "UC-005 BR-002"), never by the bare rule id.

DO NOT

• Write vague or incomplete scenarios
• Skip numbering steps in the Main Success Scenario
• Omit alternative flows for error conditions
• Leave postconditions undefined
• Mix multiple use cases in one document
• Use technical implementation details in the flow steps

Template

Use references/use-case.md as the document structure, and see references/example.md for a complete worked example — actor-focused steps, alternative flows that reference specific step numbers, and paired success/failure postconditions.

The normative definition of the format — including the German variant and the tolerances of the AI Unified Process Studio structured editor — is references/format-spec.md. A machine check of both the structure and the rules of this skill is bundled as scripts/validate_use_case.py.

Status values

Step writing guidelines

Steps describe what the actor and system achieve, never how it is implemented. Keep out protocol and infrastructure terms (SMTP, JWT, bcrypt, hashing, SQL/INSERT/SELECT, HTTP verbs, class and exception names) — those belong in the implementation, not the specification.

Workflow

1. Read the docs/requirements.md and docs/use_cases.puml.

2. Determine the set of use cases to document (one, several, or all in the diagram — see "Scope" above). Take each UC-XXX ID and name from the diagram.

3. Use TodoWrite to track progress — one item per use case file.

4. For each use case, derive the filename with the rule in "File naming" above.

5. Write the Overview section: Use Case ID, primary actor, goal, and a Status from the "Status values" list above.

6. Define preconditions — verifiable facts that must be true before the use case starts.

7. Write the Main Success Scenario as numbered steps (start at 1, no gaps), alternating actor action and system response, ending with the goal achieved.

8. Identify all meaningful alternative flows (error conditions, optional paths, exceptional situations) — most real use cases have two or more. Each one must:

   • name a Trigger that references a specific main-scenario step number, written as (step N) (e.g. Payment is declined (step 7)); and
   • end with either Use case continues at step N. or Use case ends.

9. Define postconditions for both success and failure (both subsections non-empty).

10. Document applicable business rules with BR-XXX IDs, numbered BR-001, BR-002, … within the file. Every file starts again at BR-001; rule ids are scoped to their use case (see "Scope").

11. Write each use case to its own file completely before moving to the next — never merge two use cases into one file, and never leave a planned file unwritten.

12. Run the Completeness Checklist below; fix anything that fails.

13. Final verification (do this before declaring done): list the contents of docs/use_cases/ and confirm every UC-XXX from your scope has exactly one file present, named UC-XXX-<kebab-case-name>.md (kebab-case of the diagram name — e.g. Log In → UC-002-log-in.md, never UC-002-login.md). Rename any mismatch. Then run the bundled validator over every file you wrote (the script path is relative to this skill's directory):

    python3 scripts/validate_use_case.py --strict docs/use_cases/UC-*.md

    Fix every reported problem and re-run until it exits cleanly. Errors mean the Studio structured editor cannot read the file; warnings mean a rule of this skill is violated — e.g. an implementation-level term (SMTP, JWT, token, bcrypt, hash, SQL, …) in a step, which must be rewritten at the business level: a registration or login use case says "System verifies the credentials" / "System confirms the account" — never how the password or session is handled.

14. Mark todo complete.

Completeness Checklist

The validator in step 13 checks all of these mechanically — run it rather than verifying by eye. The list remains the definition of done:

• Each file is named UC-XXX-<kebab-case-name>.md using the name from the diagram, and documents exactly one use case.
• Overview has a Use Case ID (UC-XXX), primary actor, goal, and a valid Status value.
• The Main Success Scenario starts at step 1, has no gaps, and its final step states the goal being achieved.
• At least one alternative flow exists (two or more when the use case has several failure paths); each has a Trigger that references a specific main-scenario step number as (step N).
• Every alternative flow ends with Use case continues at step N. or Use case ends. — never open-ended.
• Both Success and Failure postconditions are defined and non-empty.
• Each business rule has a BR-XXX ID, numbered BR-001, BR-002, … without gaps within its file; every file starts at BR-001 (rule ids are scoped to their use case).
• No step contains technical implementation detail — no HTTP verbs (POST/GET), SQL, class names, regex, exception names, or protocol terms (SMTP, JWT, bcrypt). See "Step writing guidelines" above.