Unit of Assurance (UofA)

The Unit of Assurance is the smallest independently verifiable bundle of credibility evidence for computational modeling and simulation (CM&S). It packages the credibility decision — who judged what, against what criteria, using what evidence, with what result — as a signed, provenance-linked, machine-verifiable engineering artifact.

pip install uofa

One command. The wheel bundles the Python dependencies, the rule-engine JAR, and an OpenJDK 17 JRE — no Java or Maven install required.

See it work — 30 seconds

uofa demo

Runs the full C1 (signature + integrity) + C2 (SHACL) + C3 (Jena rule engine) pipeline against a bundled fixture. No Java install, no LLM runtime, no internet.

The on-ramp: an evidence folder to a validated package

Four steps. Each is checkable, and the tool tells you what it could not do rather than filling the gap.

1. Extract — evidence documents to a spreadsheet

uofa extract path/to/evidence/ --pack vv40 -o extracted.xlsx

Reads PDF, DOCX, XLSX, CSV and TXT and produces a pre-filled workbook. By default this uses a local model (qwen3.5:4b via Ollama, 3–10 min per folder, no API spend). To use a remote backend:

uofa extract path/to/evidence/ --pack vv40 \
    --extract-backend anthropic --extract-model claude-sonnet-4-6 -o extracted.xlsx
# requires ANTHROPIC_API_KEY

Or with no model at all:

uofa extract path/to/evidence/ --pack vv40 --keyless -o extracted.xlsx

No API key, no network, no spend. It fills only the fields with a route measured to beat a null model that reads nothing, and leaves the rest blank rather than guessing — every blank is named in the run output. See what extraction is worth below.

2. Review the spreadsheet — this step is not optional

The workbook is a draft, not an answer. Cells are colour-coded by confidence: green ≥ 0.85, yellow 0.50–0.84, uncoloured below that. Hover a cell for its source document.

Check the per-factor levels and rationales first — they are where an extractor is most often wrong, and where a wrong value does the most damage, because a plausible level validates just as well as a correct one.

3. Import and sign

uofa import extracted.xlsx -o my-cou.jsonld --sign --key keys/my.key

Every import prints where each field came from:

field provenance: 1 defaulted, 1 derived, 2 extracted, 6 run-context

• extracted — read from your documents
• run-context — supplied by the run: who ran it, when, the input filenames, the hash and signature
• defaulted / derived — filled in for you, or computed

This is how you ask how much of a package was actually read. A conforming package can be mostly about the run that produced it, and that is worth knowing before you rely on it.

The declared profile is derived from what the package contains, not asserted — it claims what it earned. If it satisfies no profile, import says which fields are missing rather than declaring a lower one it also does not meet.

4. Check

uofa check my-cou.jsonld

uofa check runs all three. Add --explain for plain-language findings.

Why UofA?

UofA exists because the credibility frameworks are not the problem. ASME V&V 40, NASA-STD-7009B, and the FDA's 2023 guidance on CM&S credibility provide clear instructions for how to assess simulation credibility. The problem is the last mile: there is no standardized construct for packaging, transmitting, and verifying the evidence and decisions those assessments produce.

The result is predictable. Credibility decisions live in prose PDFs. Evidence is scattered across tools. Provenance is partial. Audit packaging is manual. And reviewers catch quality gaps by intuition rather than automation.

UofA addresses this through three contributions:

Standards Alignment

UofA is grounded in existing standards rather than inventing new ones:

• ASME V&V 40-2018 — Credibility factors, model risk framework, and the Context of Use (COU) concept that drives per-factor assessment
• FDA 2023 Final Guidance on CM&S Credibility — Regulatory expectations for credibility evidence in medical device submissions
• NASA-STD-7009B — CMS credibility assessment standard for models and simulations
• W3C PROV-DM / PROV-O — Provenance data model for artifact lineage
• W3C SHACL — Shapes Constraint Language for RDF graph validation
• JSON-LD 1.1 — Linked data serialization that stays human-readable

Live Demo: Morrison Blood Pump (FDA V&V 40 Case Study)

The packs/vv40/examples/morrison/ directory contains complete, working UofA evidence packages built from Morrison et al. (2019) — an FDA OSEL co-authored V&V 40 credibility assessment for a centrifugal blood pump. This is the most widely cited V&V 40 worked example.

What the demo shows:

Morrison prose assessment          →  UofA structured evidence package
  "model deemed credible"               JSON-LD with 13 V&V 40 factors,
  scattered across 10 pages              provenance chain, integrity hash,
  of journal article                     machine-verifiable in 30 seconds

Run it yourself:

pip install uofa     # bundles the rule engine JAR + an OpenJDK 17 JRE

# Run the full C1 + C2 + C3 pipeline in one command
uofa check packs/vv40/examples/morrison/cou1/uofa-morrison-cou1.jsonld

That single command runs three checks:

The bundled JAR + JRE inside the wheel mean no Maven, no separate Java install, and no --build flag is needed. Source-tree contributors can still build the JAR via cd src/weakener-engine && mvn package and run from their own checkout — the bundled JRE only activates inside an installed wheel.

What the rule engine finds on Morrison COU1 (11 weakeners across 5 patterns):

The catalog includes 23 weakener patterns spanning epistemic, aleatory, ontological, structural, consistency, provenance, and argumentation categories. Run uofa catalog to list the full set. Morrison COU1 fires 5 of those 23 — the more risky COU2 fires a different 6 patterns including 2 Critical compound rules. See the divergence below.

The compound rules fire on the output of the core rules — this is chained forward-chaining inference that standalone SPARQL queries cannot produce. Same model, same data, same rules: the rule engine reasons about the interactions between gaps, not just the gaps themselves.

Want to see the same divergence mechanism in aerospace? A parallel NASA-STD-7009B case study on an HPT turbine-blade CHT model lives at docs/examples/hpt-blade-cht.md.

The Jena Rule Engine (C3)

Quality gap detection uses Apache Jena forward-chaining rules, not just SPARQL queries. The rule engine operates in two levels:

Level 1 — Core detection rules (21 patterns) match structural patterns against the evidence graph. Categories include epistemic (W-EP-), aleatory (W-AL-), ontological (W-ON-), structural (W-SI-), consistency (W-CON-), provenance (W-PROV-), and argumentation (W-AR-*). Run uofa catalog for the full list with descriptions.

Level 2 — Compound inference rules (2 active) fire on the output of Level 1 rules:

(COMPOUND-02 ships in the rules file but is currently commented out pending design review; uofa catalog filters it from listing output.)

The compound rules are the key differentiator versus SPARQL. They reason about the interactions between gaps — something that requires chained forward-chaining inference. All weakener rules evaluate in a single Jena forward-chaining pass, so compound rules can reason over the full weakener set.

For the data shape (Minimal vs. Complete profiles, CredibilityFactor, WeakenerAnnotation), see docs/profiles.md.

Integrity Verification

Every UofA carries a real cryptographic hash and digital signature — not placeholders.

# Mint a sealed UofA (sign after edits)
uofa sign packs/vv40/examples/morrison/cou1/uofa-morrison-cou1.jsonld --key keys/research.key

# Verify integrity
uofa verify packs/vv40/examples/morrison/cou1/uofa-morrison-cou1.jsonld

Placeholder strings (e.g., sha256:placeholder...) fail SHACL validation by design — a UofA claiming ProfileComplete must carry a real hash.

COU Divergence: uofa diff

Morrison contains two Contexts of Use assessing the same CFD model:

• COU1 (CPB, Class II, Model Risk Level 2) → Decision: Accepted
• COU2 (VAD, Class III, Model Risk Level 5) → Decision: Not accepted

Same model. Same experimental data. Different credibility requirements driven by different model risk. The uofa diff command surfaces this divergence automatically:

uofa diff packs/vv40/examples/morrison/cou1/uofa-morrison-cou1.jsonld \
         packs/vv40/examples/morrison/cou2/uofa-morrison-cou2.jsonld

════════════════════════════════════════════════════════
  COU Divergence Analysis
════════════════════════════════════════════════════════

                      COU A                             COU B
                Name  COU1: Cardiopulmonary bypass use (Class II)  COU2: Ventricular assist device use (Class III)
        Device class  Class II                          Class III
    Model risk level  MRL 2                             MRL 5
            Decision  Accepted                          Not accepted
     Assurance level  Medium                            Low
           Weakeners  5                                 6

══ Weakener Patterns (8) ══
  ┌────────────────────────────────────────────────────────────────┐
  │   Pattern    │  Severity  │  COU A  │  COU B  │    Status    │
  ├──────────────┼────────────┼─────────┼─────────┼──────────────┤
  │ W-AL-01      │ [High]     │   ✓     │   ✗     │ ◆ divergent  │
  │ W-AL-02      │ [Medium]   │   ✗     │   ✓     │ ◆ divergent  │
  │ W-AR-05      │ [High]     │   ✓     │   ✗     │ ◆ divergent  │
  │ W-CON-04     │ [Medium]   │   ✓     │   ✓     │   same       │
  │ W-EP-02      │ [High]     │   ✓     │   ✗     │ ◆ divergent  │
  │ W-EP-04      │ [High]     │   ✗     │   ✓     │ ◆ divergent  │
  │ W-ON-02      │ [High]     │   ✓     │   ✓     │   same       │
  │ W-PROV-01    │ [Critical] │   ✗     │   ✓     │ ◆ divergent  │
  └──────────────┴────────────┴─────────┴─────────┴──────────────┘

══ Compound Patterns (1) ══
  ┌────────────────────────────────────────────────────────────────┐
  │   Pattern    │  Severity  │  COU A  │  COU B  │    Status    │
  ├──────────────┼────────────┼─────────┼─────────┼──────────────┤
  │ COMPOUND-01  │ [Critical] │   ✗     │   ✓     │ ◆ divergent  │
  └──────────────┴────────────┴─────────┴─────────┴──────────────┘

══ Summary ══
  COU A (COU1: Cardiopulmonary bypass use (Class II)):
    [High] 4
    [Medium] 1
  COU B (COU2: Ventricular assist device use (Class III)):
    [Critical] 2
    [High] 2
    [Medium] 2

  7 divergence(s) detected

The full report includes a per-divergence "Divergence Explanations" block with the human-readable reason each pattern does or doesn't fire on each side. The headline: COU2 (the higher-risk Ventricular Assist Device application) trips a Critical W-PROV-01 (broken provenance chain) and a Critical COMPOUND-01 (Critical+High coexistence) that don't fire under COU1's lower MRL — even though COU1 has more raw weakeners by count. The C3 engine is correctly weighting risk-driven severity, not raw frequency.

Plain-language explanations: --explain

uofa rules, check, diff, and shacl accept an --explain flag that adds a plain-language interpretation block to the structured output. The deterministic analysis remains the source of truth; the explanation is a human-readable layer for regulatory affairs and validation engineers.

uofa rules my-package.jsonld --explain
uofa rules my-package.jsonld --explain --explain-max-items 3
uofa rules my-package.jsonld --explain --explain-format json

Default backend is bundled Ollama (qwen3.5:4b, local-only, free). For higher quality or larger context, configure a remote backend in uofa.toml or override per invocation:

uofa rules my-package.jsonld --explain \
    --explain-backend anthropic \
    --explain-model claude-sonnet-5-2026
# requires ANTHROPIC_API_KEY in environment

Results are cached at ~/.uofa/cache/explain.db — a second invocation on the same input completes in <100 ms. Standalone re-interpretation of cached output: uofa explain --from-file cache.json.

Full documentation:

• docs/explain.md — usage, output formats, caching, limitations
• docs/llm-config.md — [llm] section, supported backends, precedence
• docs/security.md — API key handling, threat model

Domain Packs

SHACL shapes, Jena rules, templates, and extraction prompts are organized into domain packs under packs/. The core pack ships with standards-agnostic credibility assessment rules (23 weakener patterns). The vv40 pack provides the ASME V&V 40-2018 factor taxonomy (13 factors), and the nasa-7009b pack provides the NASA-STD-7009B factor taxonomy (19 factors, including 6 NASA-only lifecycle factors).

uofa packs            # list installed packs + counts
uofa check FILE --pack vv40                  # use V&V 40
uofa check FILE --pack vv40 --pack nasa-7009b  # combine packs

The --pack flag on any command switches the active pack(s). Multiple packs can be specified to combine factor taxonomies and rules. Per-project rules files next to the input file still take precedence over the pack default. See packs/README.md for the full pack contract.

Interrogate a Surrogate (SIP)

UofA's shift-left front door for physics-AI surrogates (ROMs, PINNs, operator-learning, data-driven emulators, ML closures). Point it at your surrogate and get a principled, auditable read on when to trust it — run it yourself in minutes.

uofa interrogate is a measurement instrument, not a verdict. It runs your surrogate against a benchmark, compares to a supplied reference, and emits a signed, provenance-bearing evidence bundle plus an at-a-glance comparison — per-QoI residuals, envelope coverage, physics-constraint residuals, UQ calibration. It never prints pass/fail: measure-don't-judge is the firewall. The output is trust-calibration evidence for you to judge.

What you supply (your surrogate stays behind one thin adapter — UofA never imports your ML framework):

# guided setup — or non-interactively for CI/containers:
#   uofa interrogate init --yes --scope sip_scope.json --output-names lift_coefficient
uofa interrogate init --model my_surrogate.onnx

# measure → signed evidence bundle + verdict-free comparison
uofa interrogate \
  --adapter sip_adapter.py:GeneratedAdapter \
  --benchmark bench.npz --reference truth.npz --scope sip_scope.json \
  -o evidence.json --key keys/research.key

Try it now on a committed surrogate evidence package (no model or data needed) — the surrogate pack's weakener catalog flags where the credibility evidence is incomplete:

uofa rules packs/surrogate/examples/airfrans/cou1/uofa-surrogate-airfrans-cou1.jsonld --pack surrogate

Reading the output. Residuals, coverage, and UQ are measurements; the pack's weakeners flag evidence gaps (e.g. an evaluation point outside the declared envelope, an unlinked residual). Zero weakeners is not a guarantee of accuracy — it means the evidence package is complete and auditable, and the trust decision is yours (uofa decision sign). In the appliance, a stock-Qwen explanation rides on top as reference annotation (decode, clearly labeled) — it explains the flags, it never adjudicates them.

The appliance (one command). The concept appliance bundles the core + the surrogate pack + a stock explainer in one container; the two-container demo feeds it live signals from a PhysicsNeMo-CFD container through the SIP interface:

docker compose up        # signals-in → explained, signed, verdict-free evidence-out

See Domain Packs for the --pack surrogate catalog, and docs/UofA_PostRefactor_Phase_A_Implementation_Plan.md for the appliance build.

Working with Your Own UofA

# Full pipeline (C1 + C2 + C3) on your file
uofa check path/to/your-uofa.jsonld

# Individual steps
uofa shacl  path/to/your-uofa.jsonld          # C2: SHACL validation
uofa verify path/to/your-uofa.jsonld          # C1: Hash + signature check
uofa rules  path/to/your-uofa.jsonld          # C3: Jena weakener detection

# Sign with your own key
uofa sign path/to/your-uofa.jsonld --key keys/your.key

# Compare weakener profiles across two COUs
uofa diff uofa-cou1.jsonld uofa-cou2.jsonld

Full command reference (extract, import, init, validate, packs, migrate, schema, …) lives in docs/onboarding.md.

What extraction is actually worth

With no model: --keyless

On five real journal papers it produces a conforming package for the three V&V 40 documents. The two NASA-STD-7009A documents fail, and correctly: 7009A defines no context of use, so there is nothing to derive a bound requirement from, and the package says so rather than inventing one.

The two trained routes need scikit-learn. Without it they report themselves unavailable and the run names the fields that went unattempted.

With a model

This section used to report F1 = 1.000 on the Morrison case, 0.973 on an aero HPT blade, and 0.964 dev / 0.954 test across a 50-bundle synthetic corpus, with "all 19 factors detected at 100% rate".

Those numbers measure detection, and detection cannot discriminate here. control_constant_list — a function that prints the standard's checklist and reads nothing at all — scores 1.000 on the real corpus and 0.960 on the synthetic one. A published credibility assessment enumerates every factor and scores absent evidence rather than omitting the row; that is what the artefact is. So any evaluation built on detection ranks a null model at the top, and this is not a corpus defect that a better corpus fixes.

The same eval reported mean overall F1 0.964 — PASS while 37 of 45 packages failed the SHACL shape.

Measured on five real journal papers with gpt-5 (2026-08-08), against annotated gold:

Two cautions that belong with those figures. Groundedness is not correctness — 0.988 says the numbers in a rationale appear in the document, not that the level assigned is right. And per-factor levels are reported as filled, not as correct: the papers grade a letter within a range (b of a-c) while the template takes an integer, and scoring one against the other would measure the mapping rather than the extractor.

The full method and the seeded-corpus work behind it are in docs/keyless-hybrid-ceiling.md and docs/extract_eval_v1.md.

To use a remote backend instead (faster, costs money):

uofa extract path/to/evidence/ --pack vv40 \
    --extract-backend anthropic --extract-model claude-sonnet-4-6 -o extracted.xlsx
# requires ANTHROPIC_API_KEY in environment

Prerequisites

pip install uofa             # CLI + bundled JAR + bundled JRE; nothing else needed
pip install 'uofa[excel]'    # adds openpyxl for `uofa import`
pip install 'uofa[extract]'  # adds litellm + pdfplumber + python-docx for `uofa extract`

For a zero-install try-it-out path, see docs/onboarding.md.

Further reading

• docs/onboarding.md — combined quick-start + architecture + contributor guide; full CLI reference
• docs/profiles.md — Minimal/Complete profiles, CredibilityFactor schema, WeakenerAnnotation schema
• docs/architecture.md — One UofA per Context of Use (the data model in tree form)
• docs/examples/hpt-blade-cht.md — Aerospace companion case study (NASA-STD-7009B)
• docs/explain.md — --explain flag deep dive
• docs/design.md — Research context + design principles
• docs/adversarial.md — Adversarial generation tooling (research instrument)
• docs/repo-layout.md — Top-level repo orientation for contributors

License

Apache License, Version 2.0 — see LICENSE for the full text and NOTICE for bundled-software attributions.

The full project (UofA ontology, JSON-LD context, SHACL shapes, reference examples, Jena rule implementations, and the CLI) is licensed under Apache 2.0. Bundled third-party components retain their own licenses as enumerated in NOTICE (e.g., OpenJDK GPLv2-CE, Ollama MIT).

Contributing

Contributions are welcome, especially real-world UofA examples from practitioners working with CM&S credibility assessment. If you are preparing a CM&S-supported regulatory submission and want to explore UofA packaging for your evidence, please reach out.

For contributors, see CONTRIBUTING.md, docs/repo-layout.md, and docs/onboarding.md.

Website: uofa.net