Schemas like Star and Snowflake serve as a logical description of the entire database, or how data is organized in a database.
Star Schema: A star schema typically consists of one fact table and several associated dimension tables. The star schema is so named because the structure has the appearance of a star. Dimensions of the star schema have been denormalized. When the same values are repeated within a table, it is considered denormalization.
Snowflake Schema: In a snowflake schema, the center has a fact table, which is associated with a number of dimension tables. Those dimension tables are in turn associated with other dimension tables. Snowflake schemas provide fully normalized data structures. Separate dimensional tables are used for the various levels of hierarchy (city > country > region).
