Answer: (i) Star schema

The star schema is the most commonly used schema in data warehouse design. It places a single central fact table (measures such as sales amount and quantity) directly beside several dimension tables (time, product, customer, store). Because the dimensions are denormalised, the join graph looks like a star, join paths are short and queries run fast — the reason it is the default choice for dimensional modelling.

The snowflake schema is a normalised variant of the star schema and is also used, but less commonly, because its extra joins slow queries down. Network schema and tree schema are general data-modelling concepts (network and hierarchical models); they are not data warehouse modelling schemes, since they do not follow the fact–dimension pattern.