What Engineering Knowledge Graphs Must Express
Context: MIN v1.1.0 — foundational ontology for engineers.
Engineering knowledge graphs face a specific challenge: they must represent not only what exists and what happens, but also what determines, what is believed, and what is uncertain. MIN addresses this through seven axes.
Axis 1: Materiality — what exists physically?
| Question | MIN construct |
|---|---|
| What is physically there? | Object |
| What happens / was done? | Process |
| What data is available? | Data |
| What arises only between partners? | Boundary |
A tensile test has a specimen (Object), the testing procedure (Process), measurement data (Data), and contact friction between specimen and grip (Boundary). All four are causally efficacious — they cause something in the world.
Key relations:
- hasInput / hasOutput — what goes in, what comes out
- hasComponent — mereological composition
- generates / generatedBy — process produces data
- describes / describedBy — data describes nexus
- bounds / hasBoundary — boundary between partners
Axis 2: Formality — what determines without causing?
| Question | MIN construct |
|---|---|
| Which natural law holds? | Lex |
| Which formal model describes it? | Structura |
| What could happen? | Possibile |
| What requirement must be met? | Norma |
| What is collectively recognized (grade, standard, type)? | Institutio |
| What is held to be true? | Epistemicum |
A materials engineer needs all six: Hooke's law (Lex), Johnson-Cook model (Structura), fatigue crack scenario (Possibile), Rm >= 270 MPa (Norma), DC04 steel grade (Institutio), and "Hooke holds here up to 200 MPa" as an evaluated hypothesis (Epistemicum).
Key principle: Forma causes nothing — but without Forma, every effect would be different. Forma is the grammar, Nexus is the sentences.
Key relations:
- governs — Lex constrains Process
- formalizes — Structura constrains Nexus
- evaluates — Norma constrains Nexus
- concerns / alternativeTo — Possibile relates to Nexus
- typifies — Institutio determines what kind a Nexus counts as
- comprises — Institutio bundles atomic Forma instances
Axis 3: Agency — who acts?
| Question | MIN construct |
|---|---|
| Who executes? | Agent ∩ Object (human, machine) |
| Which software decides? | Agent ∩ Data (ML model) |
| Which organization is responsible? | Agent ∩ Institutio |
Not just humans. A CNC machine, an ML model, a standards committee — all act selectively. Agent is a cross-category under Entity, not a subcategory of Nexus. Co-typing is mandatory.
Key relations:
- performs / controls — agent carries out process
- actsOn — agent acts on object (derived via property chain)
- owns — ownership / responsibility
- constitutes / recognizes — agent creates / acknowledges institution
Axis 4: Causality — how does it connect?
Within the world (Nexus ↔ Nexus)
- What goes in, what comes out? →
hasInput/hasOutput - Who carries out the process? →
performs/controls - What is it made of? →
hasComponent
Between world and determination (Nexus ↔ Forma)
Three generic bridge relations form the Forma lifecycle:
| Relation | Direction | Semantics |
|---|---|---|
originates |
Nexus → Forma | Nexus brings forth NEW formal determinants |
realizes |
Nexus → Forma | Nexus makes EXISTING formal determinants actual |
constrains |
Forma → Nexus | Forma restricts what Nexus can be or do |
Plus the encoding bridge:
| Relation | Direction | Semantics |
|---|---|---|
encodes |
Data → Forma | Data carries formal content (DIN document encodes Norma) |
Key distinction:
- realizes changes the world (ontological).
- confirms changes what we know (epistemic).
Axis 5: Epistemics — what do we know, and how certain?
| Question | How MIN expresses it |
|---|---|
| Who believes it? | heldBy Agent (or agent-free) |
| About what? | about Entity |
| How certain? | hasConfidence [0..1] + hasConfidenceType |
| Which status? | hasEpistemicStatus (5 values) |
| Based on what? | supportedBy / underminedBy Nexus |
| What was believed before? | supersedes (Forma → Forma) |
This is what engineering knowledge graphs typically could not do before MIN v1.1.0: formalize the difference between "42% recyclate content" and "42% recyclate content, statistically confirmed with confidence 0.92 supported by XRF measurement data."
Two complementary patterns
| Pattern | Carrier | Semantics | Since |
|---|---|---|---|
| Popperian | Process | Process confirms/refutes Forma | v1.0.0 |
| Evidence-centric | Epistemicum | Stance supported/undermined by Nexus | v1.1.0 |
Both are needed. The Popperian pattern is compact for simple assertions ("the tensile test confirms Hooke's law"). The evidence-centric pattern is needed when epistemic state evolves, confidence must be typed, or multiple agents disagree.
Axis 6: Uncertainty — what do we not know?
| Question | MIN construct |
|---|---|
| Quantifiable risk? | Possibile + isQuantifiable = true |
| Deep / Knightian uncertainty? | Possibile + isQuantifiable = false |
| Missing evidence? | Epistemicum without supportedBy |
| Dissent? | Two Epistemicum, same about, different agents, different status |
Known unknowns: "Component failure with 2% probability." Normal risk, a distribution is assignable.
Unknown unknowns: "Climate change impact on supply chain." No distribution assignable. This is not a bug but a deliberate statement.
Axis 7: Provenance — where does the information come from?
| Question | MIN construct |
|---|---|
| Who produced the data? | Data + generatedBy Process |
| Who encoded the formal content? | Data + encodes Forma |
| Who brought forth the formal determinant? | Forma + originatedBy Nexus |
| What evidence supports the belief? | Epistemicum + supportedBy Nexus |
Provenance in MIN runs through three complementary mechanisms:
- Data provenance: generatedBy traces which process produced the data.
- Forma provenance: originatedBy traces which nexus brought forth the formal determinant.
- Epistemic provenance: supportedBy / underminedBy traces which evidence supports or weakens a belief.
Axis 8: Temporality — when does it happen?
| Question | MIN construct |
|---|---|
| When was it recorded? | hasTimestamp (Entity → xsd:dateTime) |
| When did the process start? | startedAt (Process → xsd:dateTime) |
| When did the process end? | endedAt (Process → xsd:dateTime) |
| What temporal sequence? | Process chains via hasInput / hasOutput |
| What replaced what? | supersedes (Forma → Forma) |
MIN embeds temporality implicitly rather than as a separate temporal model.
Timestamps attach directly to entities and processes. Temporal ordering
emerges from process chains: if Process B uses the output of Process A,
then A precedes B. Epistemic succession uses supersedes — when a new
Epistemicum replaces an old one, the temporal dimension is captured
structurally, not through explicit time intervals.
What alignment provides:
- OWL-Time (alignment/min-time.ttl): min:Process rdfs:subClassOf time:ProperInterval —
processes can be treated as time intervals by OWL-Time reasoners.
- PROV-O (alignment/min-prov.ttl): min:startedAt rdfs:subPropertyOf prov:startedAtTime —
timestamps become visible to PROV-O tools.
What belongs in the domain layer: - Time series data (sensor readings at millisecond resolution) - Lifecycle phase models (design → manufacture → use → end-of-life) - Calendar and scheduling constraints - Allen interval relations (before, during, overlaps)
Summary: eight axes
1. Materiality What exists physically? → Nexus
2. Formality What determines without causing? → Forma
3. Agency Who acts? → Agent
4. Causality How does it connect? → Relations
5. Epistemics What do we know, how certain? → Epistemicum
6. Uncertainty What do we not know? → Possibile + isQuantifiable
7. Provenance Where does the information come from? → Data + originatedBy + supportedBy
8. Temporality When does it happen? → hasTimestamp + startedAt/endedAt
What MIN deliberately does NOT cover
| Concern | Why not | Where instead |
|---|---|---|
| Truth | "X is true" is not a MIN concept. Epistemicum says what is believed, not what is. | — |
| Bayesian propagation | Confidence propagation is a Process, not an axiom. | Domain layer |
| Time series | Temporal resolution belongs in the domain layer. | sdata-measurements |
| Physical units | Unit systems are orthogonal to ontological structure. | QUDT alignment |
| Emotions | "I feel the component will fail" is not propositional. | — |
| Self-reference | "I believe that I believe" is not cleanly modelable in OWL. | — |