In a star schema for a customer dimension using SCD Type 2, which column is typically added to support versioning of records?

• A. Foreign Key
• B. Natural Key
• C. Surrogate Key
• D. Business Key

Answer: (C)

Versioning in SCD Type 2 hinges on giving each version of a dimension row its own stable, system-generated identifier. This role is filled by a surrogate key. The surrogate key uniquely identifies every version of a customer record, and it never changes once assigned to that version. When a customer’s attributes change, a new row is inserted with a new surrogate key, while the old row remains with its own surrogate key but is marked as expired or inactive (often using start/end dates or a current flag). This setup preserves full historical detail because each version can be tracked independently, and fact records can link to the appropriate version through its surrogate key. Foreign keys, natural keys, or business keys don’t provide the same reliable, immutable versioning mechanism: a foreign key points to another table, and natural/business keys are real-world identifiers that may change or be reused, making historical tracking unreliable.