Complex schemas often involve dozens of tables, many‑to‑many relationships and varying levels of normalization.

The semantic layer manages this by defining logical entities that join underlying tables and by creating derived tables or materialized views to simplify queries.

When multiple databases or warehouses are involved, the layer can federate queries, pulling data from each source and joining it at the semantic layer.

Some platforms support cross‑database joins or data virtualization.

MageMetrics allows you to map multiple data sources into a unified semantic graph, automatically generating the necessary joins and providing query pushdown for each source.