Data layer connecting the dashboard to source systems and applying agreed metric definitions consistently regardless of how the underlying systems store raw data. Source connectors: ERP (SAP, Oracle, NetSuite, Sage via API or database connection), CRM (Salesforce, HubSpot via API), finance system (Xero, QuickBooks), product database (PostgreSQL, MySQL via read replica), and marketing platforms (Google Ads, Meta Ads via official API connectors). Transformation layer built in dbt (data build tool) for organisations that want version-controlled, testable SQL transformations: metric calculations defined as dbt models that are reviewed like code, tested for null values and referential integrity, and versioned in Git. Power BI semantic model or LookML (Looker) for organisations that want a governed semantic layer where metric definitions are centralised and reused across reports rather than defined per-report by individual analysts. Refresh schedule per metric tier: financial metrics refreshed daily after ERP posting closes; CRM pipeline metrics refreshed every 4 hours; operational product metrics refreshed every 15 minutes via incremental extraction from the product database. Data quality gate: before metrics are surfaced on the dashboard, a validation query checks for expected row counts, value ranges, and null rates; a metric that fails validation displays a "data quality alert" indicator rather than a potentially wrong number that leadership acts on.