Slowly Changing Dimensions
Slowly Changing Dimensions (SCD) is a data warehousing concept that describes how to handle changes to dimension data over time in a dimensional model. It provides strategies for tracking historical changes in dimension attributes, such as customer addresses or product categories, to enable accurate historical reporting and analysis. Common SCD types include Type 1 (overwrite), Type 2 (add new row), and Type 3 (add new column), each with different approaches to managing data changes.
Developers should learn SCD when building or maintaining data warehouses, business intelligence systems, or analytical databases where historical accuracy is critical for trend analysis, compliance, or auditing. It is essential in scenarios like tracking customer behavior over time, monitoring product price changes, or maintaining regulatory records, as it ensures that reports reflect the state of data at specific points in history rather than just current values.