When Ontologies Meet BI — Ontology-Driven Semantic Layers

Two worlds, same word

'Semantic layer' means two adjacent things in industry today:

• The modern-data-stack semantic layer (dbt SL, Cube, LookML) — a YAML/JS/LookML catalogue of metrics and dimensions on top of warehouse marts. Pragmatic, BI-first, tabular.
• The ontology-driven semantic layer (Stardog, Anzo / Cambridge Semantics, TopBraid, EKG vendors) — an OWL/SKOS ontology is the model, and queries are answered by rewriting SPARQL or GraphQL into SQL on the fly.

What ontology-driven adds

• Multi-domain navigation — a question like 'show me all Pharma products whose adverse-event signal correlates with manufacturing batch X' crosses six domains. A flat YAML catalogue collapses under the cardinality; an ontology stays graph-shaped.
• Semantic reasoning — Drug ⊑ ChemicalCompound is declared once in OWL; a query for 'all chemical compounds in shipment X' transparently includes drugs without the analyst remembering the subclass relationship.
• Enterprise vocabulary — finance, regulatory and operations teams share canonical entities (Customer, Counterparty, Trade, Position) defined once in the ontology, not five times in five YAML repos.

Where it makes sense

• Pharma R&D, financial-services regulatory, oil & gas operations, government data fabrics — domains with many interlinked specialised vocabularies that already publish ontologies (FIBO, IDMP, OSDU).
• SaaS startups with one product and ten dashboards: overkill — go modern-data-stack.

Cross-link: this track's Ontology Engineering and Semantic Web Foundations tracks teach the OWL/SHACL toolset that the ontology-driven layer uses underneath.

A YAML semantic layer is a single neighbourhood directory: a flat list of streets and shops, perfect for one town. An ontology-driven semantic layer is the Dewey Decimal classification used across every library in the country: every branch holds different physical books (rows) but inherits the same conceptual shelving, so cross-branch search ('find every 19th-century European chemist') just works. The price of that power is the discipline of maintaining the classification — the ontology — itself.