The Semantic Layer
The semantic layer is the description of what your data means: which datastores relate to which, how they join, and what the meaningful numbers and groupings are.
Where to find it
Architect Panel → Dashboards:
- Explore — the query screen built on the layer
- BI Dashboards — saved dashboards built from it
It ships inert — the engine is present and switched off until it is configured and enabled.
Why a layer at all
Without one, every report re-answers the same questions: which table holds revenue, how it joins to customers, whether cancelled orders count. Different people answer differently and their reports disagree. The layer answers once, centrally, and every question inherits it.
The join graph
The layer knows how datastores relate, so someone asking a question does not have to. That is what allows a question spanning several datastores to be asked without writing a join — and what stops it being written wrongly.
Measures and dimensions
A measure is a number — revenue, cases opened, hours booked. A dimension is a way of slicing it — by month, team, service, entity. Define the measures the business actually asks about, using the names the business uses.
Get the definitions agreed
The hard part is not technical. "Revenue" means something specific, and if finance and operations mean different things by it, the layer is where that disagreement has to be settled. Settling it once here is much better than discovering it in a meeting where two reports disagree.
Start small
A dozen well-defined measures beats a hundred nobody curated. Add when a real question needs one.