How to Build a Semantic Layer: A Step-by-Step Guide

Most teams start building a semantic layer the wrong way: they open their BI tool, create a few calculated fields, and call it done. Six months later, three dashboards define "churn" differently, nobody trusts the numbers, and the data team is debugging metric discrepancies instead of building new features. A well-built semantic layer prevents all of that. Here's how to do it right. Start With Metrics, Not Data Models Before writing a single line of SQL, sit down with stakeholders from Sales, Finance, Marketing, and Product. Agree on the top 5-10 business metrics your organization uses to make decisions. For each metric, document: The calculation : Revenue = SUM(order_total) WHERE status = 'completed' AND refunded = FALSE The owner : Who is accountable for this definition? The grain : Daily? Monthly? Per customer? The refresh cadence : Real-time? Daily batch? Weekly? This exercise is harder than it sounds. You will discover that "Monthly Active Users" has three competing definitions. T