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Data modeling · Extra High-Value

What is a semantic layer?

Mediummodel-34
semantic layermetricsBIgovernance

Question

What is a semantic layer in analytics?

Solution

A semantic layer sits between warehouse tables and BI users. It defines business-friendly names, metrics, joins, and certified definitions so people do not each reinvent "revenue" in Looker/Tableau/Power BI.

Warehouse tables (fct / dim / marts)
        |
  Semantic layer (metrics, dimensions, joins, row access)
        |
   BI tools / notebooks / embedded analytics

What it usually encodes

  • Certified metrics: gross_revenue, net_revenue, active_customers
  • Join paths from facts to dims
  • Synonyms and descriptions
  • Sometimes row-level security

Why it matters

Without it, five dashboards define "active user" five ways. The semantic layer is the contract for metric consistency, complementary to dimensional models, not a replacement for grain.

Tools people mention

LookML, dbt MetricFlow / Semantic Layer, Cube, AtScale, Power BI datasets, Tableau published data sources.

Interview tip

> "Semantic layer = governed business definitions on top of tables so metrics stay consistent across tools."

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