The star schema is perhaps the simplest data warehouse schema. It is called a star schema as the entity-relationship diagram of this schema resembles a star with points radiating from a central table. The center of the star consists of a large fact table. The end points of the star are the dimension tables.

A star query is a join between a fact table and a number of dimension tables. Each dimension is joined to a fact using a primary key to foreign key join. However, the dimensions are not joined to each other. The optimizer recognizes star queries and generates efficient execution plans. It is not mandatory to have any foreign keys on the fact for star transformation to take effect.

A typical fact table contains keys and measures. A star join is a primary key to foreign key join of the dimension tables to a fact table.

The main advantages of a star schema are as follows:

The star schemas are used for both simple data marts, as well as very large data warehouses. After the model is designed, Oracle Data Integrator can used to create the mappings and package to load the data into the star schema.