Star Schema

A star schema is a data-warehouse design with one central fact table (numeric measurements, like sales amounts) surrounded by several denormalized dimension tables (descriptive attributes, like product or customer) — resembling a star when diagrammed.

Unlike a normalized OLTP schema, dimension tables in a star schema are deliberately denormalized (a "flat" product dimension might repeat category and brand names rather than referencing separate lookup tables). This trades some redundancy for dramatically simpler, faster analytical queries — fewer joins, easier for BI tools to reason about.

A snowflake schema is the same idea with dimension tables further normalized into sub-dimensions — more normalized, but with more joins.