Semantic Layer

A semantic layer is a definition layer that sits between the warehouse and everything that queries it, where business concepts — revenue, active user, churn — are defined once, in one place, and every dashboard, notebook, and AI assistant gets the same answer. Consumers ask for metrics by name; the layer compiles them to correct SQL against the underlying star schemas.

It exists because definitions scattered across BI tools drift, and drifting definitions are how organisations end up with four numbers for revenue. The semantic layer is increasingly load-bearing in the AI era: it’s the vocabulary a text-to-SQL system needs if its answers are to match the CFO’s.

Go deeper: What Is a Semantic Layer, and Why Does Your Data Stack Need One?