Slowly Changing Dimension
Slowly Changing Dimensions (SCD) handle dimension attributes that change slowly over time, with Type 1-7 strategies preserving history.
Purpose
To design data-warehouse history tracking strategies and choose the appropriate SCD type.
Mechanism
Type 1 overwrites (no history); Type 2 adds rows + validity period (full history, most common); Type 3 adds columns (keeps the previous value); Type 6 is a hybrid. Type 2 uses surrogate keys + start/end timestamps.
Use cases
- Data warehouse history tracking
- Dimensional modeling
- ETL design