1 · Should this even be an ontology? — the 3-question rubric

The setup

OpenLearn (fictional) is a public library system publishing a catalogue of free educational resources. The first proposal from a junior team was an 'OpenLearn Educational Resources Ontology' with classes :Resource, :Book, :Video, :Topic, :Author …

The senior ontology engineer killed the proposal in ten minutes. Here's how.

The 3-question rubric

Ask these in order. Stop at the first NO.

Q1. Do I need to infer anything that isn't already stated?

Examples of inference:

• 'A reportable case is a CausalityAssessment linked to a SeriousAdverseEvent…' → yes, infer.
• 'A HighTempObservation is an observation of gearboxTemperature…' → yes, infer.
• 'A reading-list item belongs to topic Science if its subject heading is Physics' → no — that's just SKOS skos:broader traversal, not OWL inference.

For OpenLearn: the only 'inference' anyone wants is transitive broader traversal ('show me everything under Science, including Physics and Quantum mechanics'). SKOS gives that for free via skos:broaderTransitive. No OWL needed.

Q2. Do I need to constrain incoming data shapes?

If yes but the answer to Q1 was no, you need SHACL on plain RDF — still no ontology. The shape file IS the schema.

OpenLearn: yes, we'll add :Resource sh:property [ sh:path dc:title ; sh:minCount 1 ] and similar. SHACL only, no OWL.

Q3. Is the artefact mostly terms with hierarchy, synonyms and translations, used for indexing / search / tagging?

If yes: this is a SKOS Concept Scheme, not an ontology. Putting it into OWL classes would actively break SKOS's open-world thesaurus semantics — and lose the multilingual skos:prefLabel / altLabel patterns librarians have refined for decades.

The verdict for OpenLearn

• Q1: NO. (Only broader traversal needed.)
• Q2: YES, but SHACL on bare RDF is enough.
• Q3: YES. The whole project is a controlled vocabulary of subject headings used to tag resources.

→ SKOS only. No ontology. No OWL classes. Anything more would be ceremony tax.

Reaching for OWL when you need SKOS is like reaching for a relational database when you need a YAML config file. You can do it. You will spend a quarter on schema migrations to capture three settings that should have lived in 12 lines of YAML.