ashfordeOU SysML Requirements Modeling (systems-engineering-safety/mbse/requirements-modeling)
Use when the task is modeling system requirements in a SysML requirements diagram: defining requirement stereotype attributes, building the derive and satisfy and verify relationships, rolling up verification status through the requirement tree, and screening requirement text for quality gaps.
Domain quick reference
- Requirement stereotype: a SysML requirement is modeled with the requirement stereotype and carries attributes: id, text, kind (functional, performance, interface, constraint), priority, source.
- Relationships: derive (deriveReqt) links a derived requirement to its parent source; satisfy links a requirement to the design element that fulfills it; verify links a requirement to the verification artifact; refine and trace carry context through the model.
- Requirement id: a canonical id like SYS-001 or FC-0001 identifies the requirement in the tree and in trace reports; the format is checked before the model review.
- Atomicity: a requirement states exactly one shall clause; two shall clauses in one text are two requirements and are split before review.
- Verifiability: a requirement is verifiable when it has exactly one shall clause, no vague terms, and an assigned verification method (test, analysis, demonstration, or inspection).
- Vague terms: adequate, approximately, etc, suitable, and/or, as required, timely, minimize, and maximize make a requirement unverifiable because the acceptance bound is not measurable.
- Status roll-up: a parent requirement is verified only when every child in its requirement tree is verified; any failed child fails the parent; in-review children keep the parent in-review.
- Coverage: every requirement needs at least one satisfy link and one verify link; the coverage fraction is satisfied or verified requirements over the total, and the gaps are the unlinked ids.
Workflow
- Collect the requirements with their stereotype attributes and check every id with validate_requirement_id.
- Screen the text: count_shall_clauses for atomicity, find_vague_terms for quality, and requirement_verifiability for the review verdict.
- Build the relationship set: derive links from the parent tree, satisfy links to design elements, verify links to verification artifacts; check kinds with relationship_kind_valid and the derive chain with derive_chain_check.
- Roll up verification status through the tree with rollup_verification_status.
- Measure coverage with satisfy_coverage and verify_coverage and list the unsatisfied and unverified requirements.
- Combine the measures with model_review_verdict and gate the SysML requirements model review on the verdict.
Pitfalls
- Modeling two shall clauses as one requirement; atomicity is one clause per requirement, and the split happens before review.
- Forgetting the derive link when a child requirement is introduced; a derived requirement without a parent source is an orphan.
- Declaring a requirement verified while a child in its tree is in-review; roll-up only reports verified when every child is verified.
- Accepting vague wording; adequate and approximately have no measurable bound and the verification method cannot be applied.
- Counting coverage without listing gaps; a high fraction can still hide an unsatisfied safety requirement.
- Using a free-form id; the id format check keeps the trace reports and the requirement tree consistent.
- Treating a satisfy link as a verify link; satisfying design does not verify the requirement, and both links are required.
Behavior contract (gate 3)
The requirements modeling logic is exercised by the gate 3 contract test: scripts/test_requirements_modeling.py against scripts/requirements_modeling_logic.py (stdlib unittest, offline). Run: python3 scripts/test_requirements_modeling.py
Compliance
- Standards referenced, not reproduced: ARP4754A frames the requirements development and validation process that the SysML requirement model supports, and ARP4761A frames the derived requirements that flow from the safety assessment into the model; both are proprietary (SAE), summary-only per standards-map.yaml and brief 06. SysML requirement diagram semantics are common engineering knowledge.
- compliance: STANDARDS-REF, gated: false.